Decentralised exchanges will rise at the same time as centralised exchanges run by competent and regulated operators. It's getting there on both fronts but not quite yet.
For better or worse most will flock to the places that hold their hands. At the same time they'll drive out the people who are either dodgy or simply wish to remain close to crypto's original intentions.
In that case they'll be widely used but never fully mainstream. I think they'll be the decentralised Linux to the centralised Windows.
The problem with that analogy is that Linux is widely used in the business sector. The whole of Google's search engine, processing billions of searches per minute, is done on a Linux based platform. IIRC they chose Linux at teh start because it reduced the licence fees they had to pay. Lots of govt orgs use Linux for teh same reason. It's only retail users that are predominatly Windows.