If you install a 32-bit Linux, then time_t is still 32-bit, only on 64-bit Linux you get 64-bit time_t.
Although by 2038 I hope we won't have many 32-bit systems around...
Embedded devices are likely to be 32-bit for a very long time yet. I'd consider 100+ years to be a reasonable number!
64-bit devices are much more complicated (bus size, peripherals, part count) and therefore more expensive. If your entire task fits in a 32-bit space there is little motivation to use a 64-bit core.
It won't on full SoC devices but most ARM embedded devices of that sort have all sorts of peripherals which are bus connected so the bus will need to be external.
If it ain't broke...There are still 8 bit and 16 bit cores being produced today. Hoping products will become obsolete is one of the big reasons y2k was a problem.
