This is how I plan to accommodate the mitre saw. I currently have an el-cheapo sliding compound mitre saw (an evolution rage 3, which I got for the bargain price of £35 (!) from screwfix a couple of years ago when it was on sale) .  This will fit but not be level with the surrounding bench. The design is to exactly fit a Festool kapex 120 (a future purchase, I hope, but probably a few years away).

The idea is that the part shown in white flips over to form a recess that is 112mm high – same depth as the kapex saw. It will be pretty heavy, but I will try and devise some way of fixing it in either position so it does not move around.