Can we please get this? Even if it means there will be a global effects loop instead of assigning it to an effects pedal slot, it would be worth it for some of us. I bet the Axefx can do it! 
Effects loop mix via expression pedal
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+1000000. FWIW, there is an NRPN message for this, but yes a straight exp target would be awesome.
Other simple things that would vastly improve routing flexibility:
- Exp target and/or CC and/or NRPN for direct send level and aux in levels.
- Ability to send pre-amp signal e.g. Git Analog even if a loop block is engaged, so that external effects can be routed around amp block or other kpa effects.