Tony Vargas
Legend
I'm reminded of a question I just asked a PF fan in one of the PF2 threads - is there really any character concept you couldn't build in PF1 with all that's out already? I mean, prior to 4e PH3, you /couldn't/ play a psionic, but you could probably have played a character concept a whole lot like you could with RunePriest, already. So, I think, hypothetical PH4+ would have had to have stuck to new classes within the Source they introduced, only, there just wasn't much need for more classes in an already filled 'grid.'I think Tony Vargas had the best speculation if 4E had been better recieved. I think they were scrapping the bottom of the barrel for class design, but there was higher level stuff, different settings, and outer planar stuff to do.
And, if HoS and HotEC were any indication, they were not having an easy time coming up with /concepts/, never mind classes, to fill out the Shadow & Elemental sources. By PH6-9 they might've seriously regretted folding Ki into Psionics, 'orientalism' notwisthstanding.
Realistically, the direction it started in wasn't sustainable - no edition of any essentially 'list based' system is, but so much, so fast, really wasn't. Mechanically, it was sound enough to handle more and more options, clustered around new Sources, in the PH format. DMs could have, instead of the old Core Only rubric, limited the options in their game by choosing a handful of sources to allow in their campaigns, based on the setting concept. The Athas was Martial, Arcane & Psionic, for the obvious instance.Err we actually stretch a lot I think to figure out "what" they might have been the product release rate in 4e was downright unparallelled a lot was already covered.
But, realistically, it'd've had to've, if not reverse direction like Essentials & 5e, at least change direction or emphasis. Perhaps, like post-E did towards the end with HotFW, towards developing more 'Lore' over mechanics? So, more setting information rather than setting crunch, and more adventures.