I take the view that "the ECJ will rigidly stick to the EU's own laws and rules and will not deviate". If it's written down, then the ECJ will hold that what is written down must be followed. If it's not written down then the ECJ will have to decide based on which of the two sides presented the most persuasive arguments.
So you think it's possible that the ECJ could hold that the UK could revoke A50, but only with conditions attached?
No, for the reasons outlined in the previous 4 pages.
The only way conditions could be attached is if we try to negotiate with the EU27/commission in an attempt to avoid it going to the ECJ in the first place. If everyone then agrees on the conditions for revoking Art50, then it won't go to the ECJ. However, I don't think that approach is very likely to work because I don't fancy our chances of negotiating an acceptable deal, and if things like budget rebates get tangled up in it then the Govt won't be able to agree to the deal. The EU know that.
All the stuff I've written has assumed that no acceptable deal can be reached with the EU27/commission. At that point the only route is an official request to the ECJ on whether Art50, once issued, is revocable. IMV the only possible 'verdicts' are yes and no.