After a lot of rumors regarding iOS 10.3.x jailbreak, I can tell you one thing, all exploits needed to actually make a jailbreak have been released and patched for later versions, it is possible to make jailbreak for 10.3.x but here is the cold hard truth: People are making private jailbreaks, it's easier for them to not release any bugs and to have jailbreak they can use on various versions. The other truth is that Apple pays security researchers that find bugs and make jailbreaks to disclose them to Apple and not to the rest of community.
Needless to say, jailbreaking isn't dead yet, but it isn't as active as before, current situation:
- Stefan Esser keeps crying about everyone stealing his ideas (mainly blames Luca Todesco)
- Luca Todesco said he won't publish another jailbreak because community is ungrateful (thanks to Stefan Esser), he also made the infamous ABSE License (Anyone But Stefan Esser)
- Coolstar left jailbreaking community and started developing for App Store (he will still update or give away his projects on Cydia but there won't be anything new)
- Karen (angelxwind) released Phoenix jailbreak for 32bit devices for 9.3.5 with couple people (which made Stefan Esser cry again due to thinking that they did it on purpose to sabotage his Kickstarter campaign)
- Saurik is still doing his work and enjoying it, but not as active as before IMO
This is the status from my point of view, it might come or it might not, but the components for jailbreak are there already.