As long as the washing machine is outside zones and all the bathroom electrics have 30mA RCD protection then it should not be a danger. Having seen lots of washing machines in cold damp places (eg old coal sheds) I have seen a few that have rusted away due to the damp.
The machine would need a fused spur to power it and not a socket as you pointed out.
If you are buying a new CU with RCBO, then buy a spare 32A 20A 6A thereby covering cooker/ring, radial & lighting failures.
That is because they do fail, the last figure I have is 7% - but does not specify time period or environmental factors (ridiculously unless of course the sell side does not want the data known). I have had 2 failures since 2003 (both no trip on test button press, no response to Megger RCDT320 test suite).
Also ensure there is at least 1 spare way in the CU, most sparks will ensure this - but something to consider.
You could go with a 3-RCD CU, up to you, but you need a bike to get from one end to the other :-)
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