Seems slightly bulkier and 20% heavier, but that's not too bad. I wonder if the T460s panel works fine in the T460 if you're willing to do the swap.

It will, but you'll void your warranty, and it's annoying that Lenovo doesn't offer it themselves – all their notebooks are built to order anyway, so they're actively hurting themselves by artificially constraining their customers.

What about the T460p? Looks like it has the WQHD option but I can't seem to find info regarding the RAM (soldered or not).

The T460p has fully expandable RAM (almost 5 pounds), but it's a lot bulkier than the other variants (but somehow has smaller batteries), and for inexplicable reasons uses inferior materials. (Pure ABS plastic like on L/E series Thinkpads, not fibre-reinforced.)

Lenovo's model policy is somewhere between "annoying" and "fucking insane", every laptop is seemingly made by a different team and none ever talks to each other.