<…> In general too, it would be cool if there was a feature to reverse a merit within 10 mins of sending it.
I doubt that there are many cases of wrongly sent sMerit (except for a bunch of double clicked cases that lead to an upgrade to add a 60 second cool down time to remerit a post), at least not on a significant scale for it to be considered an issue to look into.
Adding a timeframe to revert the TXs would complicate things much more than it seems, since you’d have to effectively ‘lock’ the recipient’s received merits and the subsequently generated sMerits in order to avoid the recipient from spending them and then possibly needing to revert the TX in that 10 min. interval.
<…> you can always ask receiver to send you back merits, but I see no point in doing so.
No point really as you say. Besides, if the recipient account agreed to send if back, it wouldn’t exactly revert the original situation (i.e. A sends 1 sMerit to B, then B sends 1 sMerit to A to 'revert' the situation, A has effectively lost ½ sMerits in the process, the same as B. In addition, A&B would now have 1 additional (non-reversable) Merit each than in the initial scenario).