First thought is that you missed the fact that it seems Vestax have gone out of business. Which makes it highly impropable that there will be any upgrades to existing gear in the future. Also, DVS is not a little firmware upgrade, it requires quite a lot of actual electronics to be implemented. If a controller already is even remotely DVS capable, I don’t think they would keep it a dormant feature either.
As for the Denon, I can only say, you might actually come to like it better than the SX LOL. I have an SX now and I am still contemplating moving on to an MC6000mk2 (had the mk1 for a few years). It’s really got it all for the mobile DJ. The matrix inputs makes for such a flexible way of dealing with all kinds of hooked up gear, it’s Serato ready for all the announced features, it’s DVS capable, does video, has two seperate mic channels, it’s already great 16-bit soundcard has been upgraded to 24-bit and it comes in a compact 19″ size. What’s not to love if you are on the road. And it’s Denon’s proverbial “built-like-a-tank” quality.
The price difference here is less than 100 euro (about 20% of the Vestax price) and for that I think the two offers don’t even deserve to be compared, just imho of course.
Good luck with your choice.