Certainly possible for blocks that are kept (so not safecoin) or indexing also becomes a possibility over time as well. These blocks though do not necessarily hold the bits you want which is the public data map.
For SD ledger types (new, that I need to complete RFC for, but DataChains can handle this easily) then certainly a block explorer could be built, so for things like real estate transactions, government spend, budgets, speeches etc.
An SD ledger type is basically versioned everything. So will work like a normal SD, so Put on network, however with the ledger bit set, it will not delete. To update it you cannot Post it requires a Put (as you are adding data). This Put is a normal put except it’s not SD version 0, it’s an update. So these immutable updates are paid for each time.
Normal SD though is removed form disk and the chain on a new version. Otherwise it would cost too much to maintain and would be a security hole, potentially for things like safecoin etc.