So even in VMC, it sounds like a tricky situation for the enroute controller to be able to issue clearances.
One thing that has struck me about IFR pickup is this.
Aircraft A is happily going along in E airspace on a IFR clearance. The cloud is SCT and the aircraft is in and out of it and high enough not to worry too much about VFR's.
Aircraft B launches from underneath/ is crossing/ and wants to climb through A.
Centre can only assign B a level below A. They are being positively separated.
B decides to go VFR, and climb through A, whilst avoiding cloud.
Suddenly A is no longer being separated. His clearance is voided while B does his thing.
A has had no say in this, and did not want to participate in the process.
Is this how E airspace is intended to be used?
CG