Greater Anglia seem to think strikes won't be too bad:
https://www.greateranglia.co.uk/strikes scroll down and click on Saturday 1 April.
I was visiting relatives on Saturday right next to the Ely-Norwich line (just down the road from the Snetterton Horsepower control). It was supposed to be a strike day, but there seemed to be a train through roughly every hour. Didn't notice any EMR trains, only Greater Anglia - but that may be because EMR sound like normal trains and we just didn't notice them, while the whizzo new Greater Anglia trains still sound weird. There were the odd couple of trains where the driver was going very slowly though - might have been part of the strike...? It wasn't due to works or similar as far as we could tell.
I'm ECEing the 100: plan A is to cycle 100km to Manningtree, do lovely Essex and Suffolk Estuaries, cross fingers and get Greater Anglia trains home.