There are a variety of extras that may not work with SolrCloud - I don't consider any of them blockers though. Initially, I would only expect core stuff to work well until others start digging into other components. I have never looked at how the UIMA update processor plays with SolrCloud as an example. Unless a lot of people start asking about something like that, it's just not high on my priority list.
Of course, a lot of this could be done by anybody.
I look at this the same as some search components not yet supporting distrib. Some things won't work with SolrCloud to begin with as well. I've focused my attention on the core features.
Currently, anything anywhere that tries to get the local fs directory will fail when in SolrCloud mode. In the cases that you can accomplish the same thing using zookeeper, another code path can be added. I've done this for a couple other things. In some cases it might not be so easy though.
That exception is telling you, in cloud mode, this feature is not currently support - perhaps we should tweak it to be more explicit about that.
Since I'm not familiar with browse or what it tries to do internally, it's not high on my personal list, which is quite long.