This idea isn't the best, i'm sure that over 75% of players has a ping of 100ms or over. Graal is looking to increase the number of players rather than decrease the number. I think only americans has a ping that is under 100 so it would be extreamly un-fair to unable any other sparrer to queue. Yes we might have some delay but this is caused by the server so it's completely not our fault.
In addiotion, motivating players to spar by giving them rewards is a good idea. They already give top 50 players with the highest pts a trophie which could be counted as a reward. Also the NGS will provide rewards for sparrers, so admins are already working on providing rewards to Sparrers.

A good suggestion could be something like unable sparrers with a high unstable ping to queue in the spar. Because, this is when "warp" takes place, you only warp and lag when your ping is unstable. I'm sure that all sparers usually have a stable ping but, sometimes their wireless provider becomes unstable which is a bit rare to happen. I mean as many said, delay is predictable but lag isn't predictable and it only happens rarely to certain players. This suggestion will unable sparrers to queue while lagging. I'm not sure if such a thing is possible to be done but what i'm sure of is that everyone would love such an update.