Under this alleged new SNP rule, a candidate would have to resign as an MP AND CLOSE HER/HIS CONSTITUENCY OFFICE "in time to schedule a by-election at the same time as the Holyrood election". So the entire constituency staff is unemployed (odd thing to suddenly propose, during a global pandemic) and the constituents not represented for a period of months.
It's unprecedented, and it's just not sound policy-making - ESPECIALLY for the SNP, which sees HR as more important than WM in a hypothetical and wished-for transition to Scottish independence. SNP WM Depute Leader Kirsty Blackman (no Cherry ally, as she explains - but rumoured to be considering her own WM > HR move) made some good points here in advance of the NEC decision: twitter.com/KirstySNP/status/1288748079743672321
I don't doubt that Joanna Cherry COULD still pursue an MSP position if she wanted to. She'll have the savings/investments to weather a few months of unemployment, and if she somehow did resign from WM but fail to be elected to HR, I'm sure there's remunerative demand for her expertise in Scotland and beyond. She also has dual British/Irish citizenship, so the whole EU world will still be (theoretically) open to her even after it closes to most of us this December. She's undoubtedly already taken a pay cut to move from practising QC to MP, and was open to take another to move from MP to MSP. Call it political positioning in the service of personal ambition if you like (although if it is that, I don't see it as distinct from the motives of Sturgeon or Robertson), but the twaddlers wittering about how she's just out to make money easily expose themselves as clueless.
The concept that constituents would/should be angry about a by-election is pushed, and has some merit - but I'm not sure how true it is overall. First of all, Cherry was asked by her SNP branch to put her name in for the MSP position. Second, the general public seem to be in favour of by-elections even when there's no legal requirement: for example, when Douglas Carswell switched from Conservative to UKIP and when Zac Goldsmith switched from Conservative to Independent. There was considerable public criticism in the last Parliament when several MPs changed party or went independent (Anna Soubry, Chukka Umanna, Philip Lee - there were a lot more) WITHOUT calling for a by-election, even though the law did not require a by-election.
Rumour also has it that Alistair Darling (LAB) is planning a bid for the Edi Central constituency. A boon for popcorn manufacturers, if true: Cherry could likely beat him, but I doubt Robertson can. There's also the question of who will stand for the Conservatives, who currently hold the seat (Ruth Davidson is standing down). Everybody sensible is shutting up and relying on the rumour mill under cover of the fact that campaigning is suspended due to COVID; I can't help feeling that Robertson has shot his load prematurely (sorry) in all of this, and there will be a backlash.