50-55 is too low to add a "hard?" cap, but i expect there is a reason behind this.
The soft cap was implemented to slow down hardcore players progression without stopping it completely, and allow the team to get patch 2.0 out, which would then unlock new higher level content and removal the soft cap would follow. Players above the gap may gain a few levels but who cares?, if they've put the effort in and the now the new high level content is in place it shouldn't matter, the soft cap served its purpose, to allow content to be added/adjusted without creating a huge void between area's and player levels.
a new leveling system would likely follow not long after (The point system (50.1,50.2) and rebirth was discussed earlier in the project) and 50 would have likely become the new 40.
I'm sure the team are working on more high lvl content as it is severely needed. I was personally never a fan of the idea of numa/oma lair being lower lvl areas, and would of rather have implemented high lvl content in its place as i feel the content from 40+ is lacking.
My issue with a official mir layout is as you progress through the game the items/spells/dungeons increase between each level bracket (0-10,10-20 etc) until you hit level 40, when they all drop. Granted you cant implement as many spells as you gain from 30-40 as 40+ without changing the dynamic of each class and some becoming overpowered, but i believe the aspect of dungeons/items should increase each level bracket with the addition of a few new spells, which the 2.0 patch set out to cover with hundreds of new items, 2 new spells to each class ( 10 new spells in total ) and a new high level dungeon which was really 2 dungeons in one.
This content needs to be in place between each level bracket before players are entering it. there's been a few polls regarding the 50+ predicament and i believe this is most likely being worked on, aswell as the introduction of spell crafting (which is a move in the right direction, i personally love the crafting system and had big plans to expand on it which they are)
My advice would be to lift the soft cap, but make sure new high lvl content is around the corner, it doesn't need to have amazing new ai's, just new skins, new maps, new items and better exp.
If you plan to add a new leveling system for 50+ id suggest to get it in place before you remove anything, rather than putting in a hard cap that will frustrate people more than a soft one.