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!
There's more alternative infrastructure that could potentially be used: electrum-server, obelisk and probably more.
In my view however, myTrezor was (is) just an interim solution deployed while wallet devs implemented trezor support. Once enough alternatives exist, myTrezor.com can be replaced by a static page with links to supporting wallets.
So I would just run with the (almost) working BoP backend, attack those issues and wait it out. I don't know where exactly the problems stem from, but it surely casts a bad light on BoP that claims to be "enterprise ready". Graus attitude displayed here ("without BoP myTrezor wouldn't work", "you should feel fortunate") doesn't help the cause, either. The fact that communications between grau and stick are conducted here in public is not a good sign.
As always let me add that I'm tremendously happy with electrum + trezor myself, so I'm "not affected", so to speak.