Of the two, speed ramping and video stabilisation, I would say that speed ramping is the easier of the two
I am not one of the developers, but speed ramping will come, I don't know when, it's not being tested - yet ... it will come when it comes
Video stabilisation - yep that's on the list too - but the nature of the beast - how much correction you apply and how much image you use/lose and whether it can be done in realtime means that while the image may be more stable (yes, I'd find that useful too) there will also inevitably be a loss of quality.
So adding a feature can make some people happy (all of us in this thread) but upsets more people who say it's no good
Let's be honest people rarely go on a forum and see 'this app is great' comments, you see 'this app is crap, it spoilt my whole life, iM*vie is better' etc
It's a very fine balance, without even thinking about what must be going on behind the scenes just to ensure the flipping thing is gonna still even boot up when iOS 12 comes