P2PPCB mainboard mainly for bespoke / handmade keyboards?

P2PPCB mainboard Bob / Charlotte are mainly for prototyping. We can imagine mainboard mainly for bespoke / handmade keyboards. I think it should be wireless and small at any cost.

About small, I have an idea. Bottom entry surface mount female header is it (http://www.yinghuachina.com/Products/973.html). The header is 2 mm height and this is nearly equal to the height of Bluetooth module. The mating connector is 5 mm height from PCB surface. Surface mount header is fragile, but low profile worth the price in this case. Soldering IDC connector to PCB is an option, but I feel it doesn't worth because such IDC connectors have 2 mm through hole wire leads (I haven't seen surface mount IDC connector with 2.00 mm pitch) so the actual saving from bottom entry surface mount female header is just 1 mm if the PCB thickness is 1.00 mm.

About wireless, this is much harder problem than everyone expects.

The stumbling block 1: shipping

Bespoke / handmade keyboards should be shipped as complete products. Li-ion battery is almost impossible to ship with air service. NiMH battery is not impossible but notorious. Non-rechargeable battery is preferable.

The stumbling block 2: battery enclosure

We need an embedded-style battery enclosure. It should be 2xAAA and single row. Sadly, there is no such product on the market now. All available products are two row and it makes keyboards unacceptably bulky. Bespoke / handmade keyboards should not be cumbersome.

How about integrating battery enclosure to keyboard's cover, just like common products? IMHO there is little hope to make it durable, reliable, compact, toolless, rattle-less, and easy-to-use. 3D-printed resin is much more fragile than engineering plastics (usually ABS).

If 2xAAA, single row, embedded-style battery enclosure once becomes available for purchase, I will return to the idea of mainboard mainly for bespoke / handmade keyboards.

Oh, one more problem...

The stumbling block 3: first touch lag in power saving state

This is unacceptable for bespoke / handmade keyboards. I believe Bluetooth 5.3's connection subrating resolves this problem. But the majority of PC now don't have Bluetooth 5.3 yet.