As a miner, this suggestion would totally be in my own interest; however I don't think I'd like it to be implemented and I think it unlikely to be. If I'm not wrong, mining/digging speed when flying is exactly the same as when you're in midair while jumping, and it makes sense that you are slower when jumping. But, most importantly, flying at speed 10 lets you move much faster than running at speed 10: if you were able to retain the same mining speed* while moving that fast, you would be able to expose tons of ores just going straight for a while, and then mine them out; that's the most efficient way to mine for ores and you can easily imagine the consequences for economy
[EDIT]:* in my example I was implicitly assuming you would be using an eff7 pick

 

Basically impossible and a bunch of unneccisary code for no reason other than to make eff7's even more broken.