But I think, that it should be wise to drop "Bits Of Proof" if that's the "so called backend" and replace it with something more decent, perhaps "chain.com" can be a contender?
Unfortunately no other blockchain explorers understand BIP32 ...
Bits of Proof delivered a software without not a single TREZOR would have been useful or sold until now.
It supports your technology just as you wished for. It serves hundreds of your customer in every moment for more than a half a year.
You could be regarded fortunate having such a partner. Unfortunately you do not see it.
Stick you don't need a blockchain explorer to know anything about BIP32 or BIP44. Just generate 100 addresses at a time, don't show the ones with no transactions, unless the next address has transaction or a balance. Chain.com can handle this pretty easily and probably can be done all in javascript client side, not leaking the BIP32 Xpub key making it extremely more private.
They even have web hooks (
https://chain.com/docs#webhooks-receiving) that you can use to push transactions to every user using websockets and have the javascript client side parse it and update the view. You could even just websockets the addresses changed in the transactions and if that matches an address the javascript client has, then update the transaction list and balances.
You don't need a block explorer to speak bip32!