Much like animations will be a massive change for PZ, v4.0 of ORGM will be a similar massive change. This is my public To-do list.
Below is a long winded list of features and changes in the works for those curious and bored enough to read.
Post will be updated as status of various items change.

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Current Status: pre-alpha
Expected Release: Sometime after build 41 IWBUMS
Goals:


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1) Remove The Old clutter (status: ongoing)
With build 41 there won't be any save compatibility with previous versions, so ORGM doesn't need to support previous saves either. This effectively (and finally!) lets me hit the reset button on the mod, something I have been waiting to do for a while.

Many old artifacts from the legacy version and PZ's vanilla firearm system can finally be removed and restructured to better support enhanced features.


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2) Core Logic Changes (status: functional, but not fully implemented)
In previous versions how ORGM defines and stores data (weapons, ammo, rarity, etc) was quite a mess. v4.0 uses a unified 'Group' system logic for all its major features:
alternate ammo system (.223/5.56 mixing, see #4), expanded/reduced magazines (see #5), attachments/components (see #6), firearm variants (see #7) and item categories/spawn tables (see #8)


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3) Simplify Data Entry (status: functional, conversion of old data ongoing)

With to PZ's annoying requirements of needing items defined in both .txt files and lua (for weapons and magazines), and ORGM's requirements of needing extra lua for items (attachments, ammo etc) adding onto ORGM's item list has been a pain.

One of Rechambered primary goals since day 1 was to cut down on the amount of redundant data to simplify things like adding new guns.

I'm proud to say this goal has now been achieved!
Data is entered entirely in lua. PZ's script item's .txt files have been tossed in the garbage. These items are now auto-generated from the data in the lua files, massively reducing the amount of work.

To put this in perspective, a vanilla weapon (not including mags or ammo) is about 80-90 lines of work (.txt and lua).
Legacy ORGM the M16 was probably about 280 lines (.223 and 5.56 variants, both in FA and SA mode).
Current version has the M16 in 70-80 lines
v4.0 has 15 different variants of the M16, in about 100 lines, each with different features, barrel lengths, rarity etc.

The script/*.txt files may still be included in the release for better compatibility with other mods, but they will still be auto-generated.


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4) Redo the ammo system (status: not implemented yet)

Multiple changes here. For one, we need REAL ammo. Manufactured by real companies. With different stats. More calibers and types: subsonic rounds, low recoil slugs etc.

Gunshot sounds need to be tied into the specific ammo (and barrel), not hardcoded to the gun. When firing both .357 and .38 special from a revolver, you should hear the change. Subsonic shots should not produce the crack sound, with the additional ammo types this is even more important.

A system will be introduced where automatics can be picky and cycle better/worse with different ammo (just like IRL). This will not only enable realistic behavior from models such as the ruger markII that only cycles with high velocity .22LR, it will also stop a 10mm auto from properly cycling a .40S&W even though it will fire.

It will also allow the possibility of that 10mm actually working properly with a high powered .40S&W round, if the gun has a preference for low powered 10mm.
More possibilities opened by this are gas fed automatics with adjustable valves, recoil spring wear and replacements, etc.
Realistic and complex, but stupidly simple to implement.



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5) Add Expanded/Reduced Capacity Magazines. (status: functional, but not fully implemented)

Not much to say here. It works using the new Group system (after tossing out more vanilla concepts). Tested and confirmed in game.


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6) Redo Attachments/Components (status: not implemented yet)

One of the long-term goals for the mod was ditching the vanilla attachment system, and moving to a custom component based system (ie: all the major parts that make up a firearm, removable and replaceable).

Its a mass amount of work and mechanics changing (and TONS of research given the number of guns in the mod), but thanks to the new Groups logic system its finally within reach.

v4.0 will probably use a hybrid system between vanilla and the final goal. Expect more attachments and types, and better defining of what goes where, as well as expanded component bonuses/features.


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7) Add More Detail and Variants.

We all know not all Colt Anacondas are the same. Some have ported barrels, some rubber recoil absorbing grips, some are match grade, some come in .45 colt (not .44 magnum), some are rare limited editions.

Although ORGM recently introduced multiple barrel length variants, this does not go far enough. Using the new Group system and data entry methods its now simple to define dozens of variants of the same gun with different features, and not disrupt the loot tables at all.

v4.0 should add many new variants, with detailed manufacturer product ID numbers (where research and resources allow). There is currently 20 different anacondas alone, with different calibers, features and rarity.

Most people will not need to concern themselves with this added layer of detail and complexity. It is there for the OCD details types and collectors, and will include many rare limited edition models.

As well as variants, more guns in general should be included. But sorry, I won't get into specifics yet.


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8) Redo The Spawn System (status: functional, but not fully implemented)

Even with all the changes Rechambered provided to the spawn system, the core logic (civilian/police/military + common/rare/veryrare) was still a legacy artifact.

New system will be easier for map modders to expand onto for custom rooms, and uses the new Group system to seriously expand and refine how weapons are spawned. They can now be spawned any which way:
by model (anaconda variants), by manufacturer (colt), by manufacturer and class (colt revolvers), by class alone (revolvers), etc.

Spawning a colt may decide to spawn a colt revolver (or pistol, or rifle, depending on spawn weights), and then might decide to spawn a anaconda...then picks a variant.

The loot should be much more natural then random piles of whatever.


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9) Redo the UI (status: on hold)

Got some ideas for this, not going to share them yet. But with the increased complexity of the mod, something need to be done. Tooltips and context menus are not sustainable long term.
We'll see how much time I have to work on this (no promises)