As a veteran crafter who has multiple mules edging ever so closer to 100 crafts, I personally see no reason not to lift the cap. As a matter of fact I welcome it because it would turn many synths into 11 31 51 tier HQs, specifically synths that are held back by their subs from attaining certain HQ tiers. That's exactly what I would do with my character, and not go with 2 100 mains.
I really can't see any down sides to it. Crafting is alive and well where I'm standing. People are just bitter their gold mines have been cleaned out. Mines that were the only reason they bothered crafting. I wasn't happy either but I moved on. We all know how that junk went. You did wood for staves. Bone for Scorpion harness. Leather for sniper rings. Gold smithing for.. well, pretty much to be filthy rich. Cloth for verms. Cooking for sushi. Smithing for haubs. Everything else was a side bonus to the big synths. And I can't say I blame them, but it was headed that way anyway after the inflation period thanks to gil sellers. People bought a ton of gil and got those 100 crafts.
Whatever you guys choose to do though, I think I speak for everyone when I say let the crafts do their job and not so much synergy doing it for them. Don't give up on Synergy. Don't get me wrong here. I'm just saying, the crafts deserves some of that fancy new gear that rakes in some serious gil to replace the ruined money makers of old. And I say that as a 80 synergy atm. I'm not wanting the synths out of self need. I just think the crafts deserve better and I see no reason a 100 craft can't produce level 90+ gear and with HQs to go with it instead of not at all. Wood in particular is in dire need for something worthwhile as magian has destroyed it's HQ market. Nin tools are not an acceptable replacement, nor is warp clubs, nor is HQing lumber...
I'm tired of seeing new synergy gear being a monopoly by a handful of players for several months after it's released. Hey they did the work, they deserve the payout, but still. Even if I were one of those making a ton of gil thanks to synergy, I still would feel that crafting deserves better and the players that have taken the time to raise a 100 craft darn sure deserve better than a handful of people on an entire server making out like bandits after every update for months. You shouldn't be forced to level synergy to compete. It needs to be a side bonus to crafting, not a necessity, no matter how easy it is to level. In other words, mix it up. Don't play favorites. Give crafting some big synths and synergy some big synths.
One worthy note to make about all of this, Ebon gear was sorta in the right direction. It used the crafts to form the base gear and used synergy to enhance it. I would like to see more of that in the future and less of the 'let's give synergy everything worthwhile' approach.