Should we still use the media_upload_tabs filter to add tabs in the Media Manager after WordPress 3.5?
Unfortunately it's very difficult to predict whether or not someone will make changes in WordPress, as an Open Source project you yourself could make that decision, contribute code and have the outcome you desire to some extent.
Fundamentally however the old adage 'if it ain't broke, don't fix it' applies here.
It is hard to know from your question exactly what you are trying to do but there is a lot of criticism by the community as the Media Manager is now very dependent on jQuery and JavaScript and so you may have trouble implementing your functionality in the old way.