Like you, I would love to see the the advancements of the 16" model rolled into the 13". However I also feel there are opportunities for the 13" to leapfrog its bigger sibling and maybe this is one area where that may occur.
I would be particularly keen to see just a little more depth to accommodate Cherry ULP switches as discussed here, here and here, to reference just a few threads. For the price of just a little more thickness the benefits of discrete switches for repairability, key feel and and custom keyboards can be ours.
I consider it regrettable that Framework did not make provision for these switches when they came to design the 16" model as it would have infused the “Framework” philosophy into the modules themselves. When the time comes to redesign the chassis - or offer upgrades - of the 13" model to incorporate lessons learnt from the bigger sibling, and I am determined that discrete switches are considered.