Yeah, they accept patches at their forum http://neosource.1emulation.com.
They have a repo but private (for known contributors.) Alternatively, pm dink on there.
Some information about the current state of rerecording in FBA (and what would be needed to add to make it a viable TASing emulator in order):
* Deterministic replays. This is the biggest issue: currently replays will only start recording from a savestate. After asking, recording from power on (without savestates) was disabled because it caused crashes.
There is an incredibly hacky workaround for this (but it works!): load the game, then click outside the FBA window (anywhere on the desktop, from example.) After this, the game will be paused: from there, select Game > Record input and record your movie as normal.
Implemented, press F1 - bindable to other keys.
* Read only & Read+Write functions - not implemented.
* Ability to bind savestates to multiple slots - currently you can only bind them to one slot, and have a separate hotkey to switch slots.
The file format used is the same one as in blip's rerecording builds (fr). I've made a page about it.
For the rest, the implementation is solid in general (it doens't shit itself on Neo Geo, for example, and syncs properly on CPS1/2/3) and FBA has support for more games, such as, for example, Neo Geo CDs.