I like where this is going!
So do I. :D
What excites me is the 999 MP limit removal, that for some reason irritated me because the game could allow you to get higher but prevented you from keeping it. Now I just need to figure out how to rewrite the game's assembly to allow spells to have a separate byte for MP cost and ignore walls-right now they share it. Which in-turn means you can only have a maximum of 127 MP cost for a spell since ignore walls has a bit of 0x80. Still, 127 MP is plenty if you consider the natural MP evolution for any character doesn't go past 981~983 (Rydia). You'd have to actually rewrite the level up data for these characters to allow for more MP growth, which would actually rock me thinks...
That way Bahamut and Meteo won't be guaranteed 9999 max damage attacks but go beyond that. Finally something for those larger spell multipliers to be used for.
Indeed, there are a bunch of attacks/spells/skills that can easily go beyond the 9,999 damage limit. Throwing an Excalibur for example does between 12,000 and 14,000. Jump on non-Aerial weak targets does between 11,000 and 16,000 damage (with maxed attack/str stats). White/Holy (which is more powerful than Nuke) can do 11,000 to 14,000 (or so). When you berserk Cecil, Cain, or Edge and they have over 200 attack (with 19x multiplier) + 99 Strength they can perceivably do 12,000 to (and over) 15,000 damage.
Though can the FFFF amount of HP be increased? When dealing 17000 to 20000 damage it's probably not good to keep enemies at their base maximum 65,535.
I'm sure FF4 can support a 24-bit monster HP but it would require probably as much or more assembly changes than FF6 did. FF4's monster data is variable length and not fixed length like FF6 (and FF5). What's I've tested is having a max of 16,000 (or 15,999) damage seems to be a bit more realistic for FF4 simply because it actually takes a bunch of high stats to even get over 9,999. For example, when you watch my video Cecil's White/Holy doesn't even hit for 9,999 and he has max magic stats. o_O
Oh, and I've found the stat limit for your normal stats but of course the game for some reason won't let you get past 99 STR/AGI/VIT/WIS/WILL. This though would be good for ROM hackers wanted to actually limit stats for balancing purposes. Imagine having a limit set of 50 on all stats, that would make for a good hard challenge version. Which I'm planning on revamping my FF2usHT with this new data with changing the 9,999 damage limit cap to something lower.