Powerbank usually means a battery pack, if that's what you meant.
And about making those ports optional - it would be ultra-cheap and ultra-simple to just daisy-chain another TB3 device to the PCIe adapter. It would be like 10x cheaper than having a special space for it in the adapter, and would make it much more portable for those who don't need both. What do you think about that? If you only use both of them, just leave them daisy-chained at your desk, and connect the loose cable to your PF whenever you want to use them. Or you can disconnect them and use only whichever you want.
And I want to have only a PCIe adapter, for exactly the reason you named: using it with other products. Laptops with thunderbolt often already have an ethernet port and plenty of USB ports, so there's no need for expansion. Of course this doesn't apply to me, because TB3 is a totally unnecessary luxury for me (unless we pull this off and make a PCIe adapter for under $80), but I can see how people using other products would NOT want these extras they don't really need. If you want, you can daisy-chain them, it's up to you, but we shouldn't force others to pay more for what they don't need.