using a 256GB SD card on a phone that only advertises 32GB capacity right now... works fine.

but phones that advertise low capacity limits are probably also not wiring the SD interface for high bandwidth. it's not unusual to see internal flash capable of 100MB/s but SD interface only capable of 10MB/s :(

Capacity limits for drives exist because the maximum capacity of SD cards depends on the protocol used: SD, SDHC, SDXC, SDUC. Each protocol requires driver support in the device. Hardware wise, there isn't many changes required though, and to some degree this partitioning is also artificial because one can just make a standard that supports horribly gigantic capacities.

But anyways, the limit exists, and this means that whether your device can support larger SD cards after it is released depends on whether the driver is getting updates or not. Android phones are quite known for not releasing driver updates, although often there is updates for Android phones as well. Thinkpads are IBM computers, and the update story is way better there.