In no special order;

* Allow youtube embeed to start at t=time
* Support playing GIFV links even if Steemit isn't hosting / caching them.
* Show beneficiaries on posts (monetary lost vulnerablity)
* Allow beneficiary on create post (netuoso steemliberator already does that nicely)
* Show vote value when casting a vote
* Show vote values breakdown in on posts
* Put back the downvote button (without some annoying warning, Don't allow vote weight to make a post below zero on downvotes.) https://steemit.com/steem/@transisto/improving-negative-curation-a-downvote-button-vs-flag-explained-condenser
* Show important financial information properly in wallet page. 
  * Power down vest received
  * Change of withdrawal routes (monetary lost vulnerablity)
  * Fix transfer display problems, (monetary lost vulnerablity)
* Have a go to user search box that basically replace the input to steemit.com/@input editing out URLs is for nerds.
* Upgrade markdown WYSISWG editor.
* Shorten time-frame used for sorting tags to make it more dynamic. (#LIFE, and  #steemit have been pegged up there for way too long)
* Filter out 0.001 transfers in wallet https://steemit.com/steem/@transisto/steem-improvement-proposal-minimum-threshold-for-being-notified-of-transactions-memo-messaging
* Include or link to a Revision history view. This should have been done before enabling EDITS. Isn't immutability  blockchain's most prized feature?  https://github.com/steemit/condenser/issues/3043

Is there anything contentious in there or that risk breaking the chain? As far as I know all of these are purely UI issues and don't break any consensus rules.

What's the hold-up? Why isn't Steemit throwing ressources at it's supposed core product/interface? The blockchain's development is decentralized right? 

Nobody will ever use the first two content type if Steemit isn't displaying them properly and it will drag down progress for all other front-ends.  Dmania's main feature was to display GIFV files instead of being limited to large inconvenient GIF files, Why not spend 1/100th of what was rewarded to dmania via delegation to fund GIFV 
 support in condenser?

https://www.youtube.com/watch?v=IkXFfNzpPnw