Again just because the numbers easyjet has suggested they would happily fill an ATR or dash it doesn't really work like that.
With Ryanair (offering fares as little as £20) and easyjet operating STN - EDI with a total of 6 flights a day from October then you have LCY which has BA citiflyer flying loads of sectors each day plus from October Flybe themselves will start operating the LCY - EDI.
So if you really that a good look at it would SEN - EDI be viable at this present time, I would certainly say a big No!
In fact in that part of the world flights to EDI are starting to look over saturated!
Please don't think I'm being rude but you have to look at all the factors why they haven't done this particular route from SEN