In reply to Removed User:
First of all, I don't think they will do that. I think the EU will avoid this confrontation and offer another 3-6 month extension subject to a set of criteria (presumably a GE).
Reasons for following the above course of action:
it forces UK parliament to make an actual decision: revoke, WA, no deal. Parliament seems to be against no deal at the moment, so it could be good timing to force the issue. The WA is the most likely scenario and also the one the EU27 favours. EU27 can live with revocation if they have to. No deal would be bad, but manageable for the EU27 resulting in the WA anyway.
The EU27 public would be happy with it, because everybody is getting fed up with brexit and its lack of progression ( I know, I know, in the UK this is even worse ).
Telling all businesses to prepare for no deal and then extenting again is costing money. If no deal is going to happen, from a business point of view the date where we are actually preparing for is better than other dates. The extension of the Apr 1st deadline was expensive in this regard.
The EU27 has a running cost in extension as well. This is mostly council and parliamentary time devoted to brexit that could have been used for other issues.
Finally, the EU should avoid being seen in a geopolitical context as too weak to exert power over neighboring states. If, e.g., the EU sets a deadline to Marocco, it wants this deadline to be taken seriously and not have the rest of the world assume that the EU will extend anyway.