Selecting rows like that is very similar to how DRAM works, just with the word size being the number of subpixels in a row, and with no read port. Bit-level random access is inefficient, but you don't have to write to the rows in sequential order, and you don't have to update all the other rows before issuing another update for the first row. That's purely a limitation of the current driving circuitry, but a replacement like G-SYNC doesn't have to be bound by sequential rasterization any more than it has to stick to a fixed refresh rate.