On number 2 - I wouldn't call it "cryptocurrency" first but rather (and forgive my lack of articulation here) crypto/defi/blockchain first.
Think of crypto like the new internet protocol - rather than equating it to gold. But unlike the internet protocol, this extends much beyond e.g. crypto is wealth, an application, a service, a medium.
This means a whole new set of services and revenue streams / protocols on revenue (from selling products) and expenses (guessing these get built on a host of defi applications). All these integrations - will XERO focus today? Nope. Is the potential market for this massive - yes, well if you are bullish crypto.
Early examples of companies that would use this - https://upland.me/, https://nbatopshot.com/
Crypto-assets are variously regulated more as property, commodities or securities; and from an accounting perspective I don't think that's a distinction that can be willed away.
For example, there are just certainly tax implications that won't be accurately recorded if you assume that income of 1 BTC offsets expenses of 1 BTC. My understanding is that the IRS wants you to calculate the USD fair market value of each of those transfers at the time they occur in order to determine the tax implications.
Q–1: How is virtual currency treated for federal tax purposes?
A–1: For federal tax purposes, virtual currency is treated as property. General tax principles applicable to property transactions apply to transactions using virtual currency.
Q–2: Is virtual currency treated as currency for purposes of determining whether a transaction results in foreign currency gain or loss under U.S. federal tax laws?
A–2: No. Under currently applicable law, virtual currency is not treated as currency that could generate foreign currency gain or loss for U.S. federal tax purposes.
1- the internal accounting system. This is not really different from the traditional world, it can be done with most accounting services already. The company I work for (OneStream) focuses on consolidation/planning rather than low-level general ledgers, but handling crypto would just require to use a custom currency (I think we allow up to 7 or so). Managing exchange rates can be done in actual code, so you’d just set up some api calls to decide how you want to calculate those rates and be on your way. I honestly don’t see anything crypto-specific here. The only annoyance would be seeing loads of “0.00000...” in a naively-setup system, but that can also be dealt with trivially in most services.
2- external integrations. This is really where the hole in the market is, I guess, and probably what motivated you to explore the space. Services that will automatically pull your transactions from cryptocurrency exchanges and similar hangouts, might be thin on the ground today; I honestly don’t know. But consider that, for the likes of Xero, because of point 1 above this is basically just a bunch of plugins that are fairly trivial to write, should they decide to steer. If they solved “legacy” banks, they can solve online banks pretty quickly.
So, would a product focused on 2 be successful, in a market already crowded that can probably self-extend to crypto fairly easily? I’m skeptical, personally, but I might be wrong. I’m also skeptical that significant numbers of businesses will go “cryptocurrency-first” and look for such a service. Cryptocurrencies are more like commodities than actual currencies, and I bet no company is “gold-first” in 2021.