Just give the users the option to query chainz. It is after all their security in their own hands. And I trust chainz enough... especially if you
get 2 other decent block explorers it can poll.
Presumably a faster solution but it sounds a tad centralised by it's nature of being reliant upon 3rd party APIs.
In the long term I would prefer the SPV approach championed by Synechist as it's more in spirit of what's been accomplished thus far. However, I'm also grateful for any and all development and querying an API service does get the job done.
I think 3rd party open sourced APIs should be fine for the short term. Similar to how a lot of us don't run the bitcoin software, but use an open source wallet to interact with the network.