I was an early adopter of the Motorola Xoom, since it was the first "real" Android-based tablet. It came with a non-functional SDcard slot, which was promised to be enabled "with a future update".
I think (my memory could be wrong) that it took Motorola nearly a YEAR to implement support for that slot. So yes, not putting too much weight on promised "future features" is a good idea. In the case of the WRT1900AC however some people were mislead, since the router was marketed as being opensource-ready, not as "will eventually get OpenWRT support". A lot of customers who specifically wanted to run OpenWRT or DD-WRT only discovered after their purchase that it wasn't possible yet, and there was no ETA for it either.