I agree that defining a money type is somewhat ‘better software engineering’ when looked at it some ways. But I see the future of Bitcoin Core as just Bitcoin Core, not ‘Altcoin Core’.
Eventually I want to enshrine the Bitcoin-specific consensus code in a library that as is as small and independent as possible and completely specific to Bitcoin. Altcoins can create their own consensus libraries. I expect there to be little or no code sharing between these. The consensus code does not need to be general.
For this goal I think inside the consensus code it is good to have more low-level concreteness, not more abstractions. Recently we already went from the CBigNum type to well-defined, concrete uint256/uint160/CScriptNum types.
However in the rest of the code that interfaces with client applications (RPC), or the user, or provides some other interface, a more abstract interface that isolates from the specific representation of money inside the system is useful.