Longtime simmer (Warbirds 2.xx, Aces High Beta '99, MSFS 1995+, Targetware) with a few bits for the devs to ponder on...
Refined visual effects. Any number of YouTube videos can be referenced for show-of-force fly-bys, gun employment, engine blast/rotor wash, etc. Muzzle blast is a bit simplistic, moreso at night. Engine blast, rotor/jet wash, and aircraft wake all create rather pathetic dust/water effects. Just needs a bit of polish, really.
Aircraft functionality before complex systems/weapons implementation. The F16 'pinky switch' for afterburner gate doesn't work but we just received ECM, HMCS updates, HTS, and other complicated systems.
Standardize control mapping for common functions. Having to tell DCS I don't want my CH Throttle mini-stick to function in pitch/roll, but do want it as the TDC slew, for ten separate aircraft is needlessly complex. Multiply this by... CH Throttle, VKB Gladiator, seven separate hat switches, eight buttons, one two-stage trigger, and a button box. Right now, four of the seven planes in FC3 aren't even mapped because I won't spend an hour repetitiously resetting functions.
A patch or two per year for bugs/issues/missing bits in modules that were called 'done' but weren't actually finished. F5E has had broken instrumentation for years. Yak doesn't have LOD models or a damage model, again for years. This is rude to customers who paid for a complete, functioning, module and then didn't get it because the Next Big Thing hit the pipeline as a money maker. I have some miles saved and after watching Mover's various commentary on the T38, was going to get the F5E. Then I went through the bug board pre-purchase and got cold feet. Now? Likely save them for the A6E when it hits. If long-standing issues are being addressed, or the modules are being updated ala BC3, ED needs to state as much in a pinned news post.