First off, thanks for using the mod, I'm glad you like it! I've been trying really hard to make it feel properly "Ultrakill"

Secondly, Railcannon is in the plans, as mentioned this guy is still pretty early in development. I'll get to it, just bear with me on the time.

In regards to spammable projectiles, the Marksman shot was designed to be somewhat similar to Megaman's jab in Smash, it's fast, low damage and low hitstun. You'll notice you don't really get much off of a Marksman shot.
Piercer, on the other hand, is a f9 startup iirc

Other than that, I'm talking to a lot of other mod developers to tweak the balance as I go, so your friend can rest assured that the projectile abuse is something that is being actively taken into consideration. V1 is meant to have good projectiles, he's a hit and run sorta semi-zoner. But of course I'm gonna be keeping an eye to make sure they aren't ♥♥♥♥♥♥♥♥ either.