Just an idea, but I think it is worth implementing. If you want to get a block explorer, it requires storing the whole chain. That means, you need to have all blocks, and maintain full archival node, if you want to run a block explorer. As blockchain gets bigger and bigger, people no longer can use their internal HDD or SSD, permanently attached to their machines, because many devices have 256 GB or 512 GB storage. That means, some external disks are needed, for example connected via USB.

So, what is the problem with external disks? Well, they are sometimes disconnected by the OS, for example when Bitcoin Core downloads a lot of data into memory, and processes all of that, without doing any I/O for a long time. Which means, some unexpected I/O error could easily kill Bitcoin Core, and then you end up reindexing the chain (which takes a lot of time, even if you have for example the first 500 GB already downloaded, and stored on your external disk). That also means, if you cannot turn "energy efficient mode" off, you are forced to monitor your Bitcoin Core client, and restart it every sometimes, just to dump everything into your disk, before your OS will detach it, because of external disk inactivity for N minutes.

That means, the final setup looks like that: there is a full archival node, sitting on some external disk, just to be safe, and to have the whole blockchain, just in case. But on internal disk, on which OS is running, there is some pruned node, for daily operations. Also, when it comes to nodes running 24/7, those nodes usually can be placed on some servers, but their storage is usually not so big, to allow storing the whole chain. Which means, only a local node on external disk is full archive node, all other nodes are in pruning mode.

As blockchain gets bigger and bigger, we can expect there will be more and more pruned nodes. Because using external block explorers is unsafe, it is usually a good idea to have your own block explorer, and just import addresses as watch-only, if you want to explore them. However, if your node is in pruning node, then some commands does not work, for example importing addresses, because there is not enough history for a full rescan. Which means, to have a full functionality, it is still needed to attach some external disk, and ask full archival node for some proofs, to import them into pruned node.

However, pruned nodes already contain a lot of useful information. For example, each pruned node can verify, if a new incoming transaction is correct or not. That means, each pruned node contains a full UTXO database. And very often, what users really care about, is not the full history, related to some address. Users often just want to observe only some unspent transaction outputs, and not dig into the whole history of past transactions, and spend transaction outputs. All of that leads us to the idea from the topic: having UTXO explorer, instead of block explorers.