Using the GUI wallet and the RPC wallet it is possible to create a transfer across sub-indices of the same account.
But the subaddress documentation indicates that it should be possible to create a transfer across multiple accounts in the same wallet:
Thus, a single transaction can - in principle - aggregate and spend outputs from multiple addresses (and by extension from multiple accounts). The CLI or GUI wallet may not directly support creating such transactions for simplicity.
I do notice that last sentence - indicating that the functionality might not be implemented.
If I look at the RPC wallet transfer command it only allows a single account index.
Is there way around this?