Hello,
well, in real life, you would put down your card and say "Belote". Another person wouldn't have the opportunity to play faster than you, unless of course you really forgot.
I think that's the main point Sylphrena was making, if you forgot the announcement, too bad, but if you didn't forget the announcement and just weren't fast enough (either because of your connection or because of playing from a phone), then you shouldn't really lose it.
Unlike Uno this shouldn't be a game of speed as much as just making sure that you really want to do it.
When this mechanism was released in Tysiac, I actually wanted to suggest the same, but the main thing that made me not do it is that the rules explicitly say this:
If a player owns the king and the queen of trump, their team can obtain 20 bonus points. To get them, they must announce "belote" when playing the king, and "rebelote" when playing the queen, just after having played the corresponding card but before the next player plays.
If this suggestion were to be implemented, that would invalidate that second part of the sentence, as it wouldn't even be possible for the next person to play before the announcement is made. Personally I don't think that's necessarily a bad thing though, as I think it's more important to make sure the announcement isn't forgotten, rather than you were the fastest person to press Space.
Then I was also thinking that it would probably be necessary to keep backwards compatibility. The reality is that the majority doesn't read the forum or the updates topic (which is itself often not updated), so it would be quite a nasty surprise to find out that pressing space after you played no longer works and you were actually supposed to do Shift+Enter, so you lost it. That's mainly why I'm personally not a big fan of changing something that was established for a longer amount of time, but that's just how I see it.
PS: Shake the device feature may be useful here, except that actually shaking isn't mapped to saying Belote/rebelote in this game.