On the Commodore 64, there is a 12 bit datapath between memory and the VIC II: the ordinary screen data, which is in DRAM, and another 4 bits which comes from another SRAM chip which may be paged into the CPU's address space. This area contains colour information.
It's occurred to me that exactly the same could be done on the ZX Spectrum, so that the ULA, or whatever hardware generates video, could get at both pixel data and attributes quicker. That could mean not needing to slow the CPU down. Or it could mean being able to use a slower DRAM for cheaper. But it would mean needing another 8 bit wide memory. Maybe a couple of 2114s or something.
Is there any ZX Spectrum or clone that works this way?