@monte, I've implemented in PR https://github.com/mysensors/NodeManager/pull/517 something going in the direction you pointed out. Before explaining just a simple assumption first: NodeManager is intended to run on a number of different boards, most of them with limited memory so this capability has to take this constraint into consideration (hence no json parsing, reuse of existing communication mechanism, capability disabled by default, etc.)
Apart from this, I found a sort of compromise to enable/disable sensors, even remotely and optionally persisting the status across a reboot. All the implementation details are within the PR (down below, the PR also include other enhancements) feel free to provide comments here or on Github. Hope it could be useful to avoid reimplementing the entire logic from scratch
I think you can just set the I2C pins in MyBoardNRF5.h without remapping the pins in MyBoardNRF5.cpp.
Look in MyBoardNRF5.h, under the Wire Interfaces section. Set SDL and SCA to 30 and 31 as appropriate for your board.
