Well, some currently used BLD formats already have that property. I've been at a competition where you would get a 2nd and 3rd solve if your first was under a certain time, DNF or not. So if you were slow, it would be in your best interest to DNF quickly, because then you could have 2 full attempts instead of 1.
To be honest, I'm not really sure I see a problem with either (a) rewarding people for a bad result, or (b) asking scramblers to do extra work - at least not in the 3BLD round. Issue (a) isn't a problem because nobody will get 100% successes at full speed, and so if you want to do any kind of combined-final type round but not introduce too much luck you basically have to look at the time of the solve and ignore whether it was a success. Of course, by that metric a 2-3 minute DNF is definitely better than a 6 minute success. Issue (b) isn't a problem because BLD solves take so long (2+ minutes for a typical competitor) compared to the scramble time (<10 seconds - negligible for all intents and purposes) that at all but the largest competitions you can have a single scrambler and they won't even be very busy. In fact, as someone who often helps out at the scrambling table, I'd rather apply a lot of extra 3x3 scrambles than wait around for the last solves of the inevitable slow solver who didn't start until the round was pretty much already over.