I agree with the summary from @dprat0821 above, but would like to add my 2c.
Openness great. Privacy needs new tools. Performance is important but adequate for now.
Replication mentioned, I would classify as performance improvement similar to caching, very similar to web caches we’ve had for a long time. Their legality has been tested many times over, but seems to have subsided. Caches are well defined and cache coherency protocols don’t need to reinvented.
I also disagree decentralization helps with privacy directly or that it is very difficult to harvest lots of data. Yes, it is more difficult than querying a centralised DB, but only slightly. Just look at google indexing the web for an example.
The great benefit of Solid is the openness of the data. The data is mine, I can copy it, I can delete it, I can edit it, I can also use for new purposes. The data also belongs to the app that created it. More work is required to reconcile the shared ownership, though.
Improved Privacy will need auditing applications (not there yet) and permissioning templates, but they will be possible if the data is visible, not walled only for the app benefit. At the moment standard ACLs are too granular for normal users, even power users will struggle maintaining a lot of differently shared data. But it can be worked on right now. Takers ?
Re Performance : it is a valid concern, albeit secondary so far. I don’t see a conflict and the caching mentioned is implemented already in one of the access libraries as far I understand.