16Mb of flash and 64Mb of RAM is typical. There is always more RAM than flash a new image can be downloaded to RAM, then burnt into flash. Embedded systems of this size running CIFS and Windows printer servers are very common. In fact vendors are now starting to drop their home brew solutions and base their stock firmware on OpenWrt, which is very pleasing to see. It means manufacturers like Broadcom and Atheros are being dragged into the open source world.
Anyway, my point is there are now substantial revenue streams dependent on Samba running on these devices. That means regardless of what the Samba development team decides, one of two things will happen: either Samba v4.0 runs on these devices or Samba will be be forked into v4 and v3 streams.