The PC architecture, from the original IBM PC onward, has always been designed around the idea that video memory will be on an expansion card. This was an unusual design decision; most 80s computers did not do it that way. It has advantages in terms of easier upgrades, but can have the disadvantage of making it slower for the CPU to write to video memory.
Of course nowadays, that doesn't matter because you're not supposed to use the CPU to write to video memory at all; that's the GPU's job. But I'm thinking about the 80s and early 90s, when the CPU still did all the work.
Now, there are always going to be wait states during active scan line, because the video chip is using some of the video memory bandwidth for generating the display; that's true regardless of where the video memory is. (Unless you have dual-port VRAM, which was expensive and rarely used.) I'm not talking about that here.
I'm talking about wait states incurred by the CPU writing to video memory, even outside active scan line, because it's on an expansion card at the other end of the expansion bus, as opposed to main memory on the motherboard.
When did video memory start incurring wait states for that reason? For example, I would expect CGA not to do so because the original IBM PC actually put main memory beyond 64K into expansion cards on the ISA bus. But what about EGA? VGA?