I would like to be able to track Threat percentage in the same way Tiny Threat or ClassicThreatMeters does, but customizable.

I just want to be able to track my own Threat percentage in an easy and customizable way. If other addons can track threat for the entire raid why cant i make a threat tracker based on my target for my personal threat?

The game does not give an easy API for this information, and there are several incompatible solutions for threat implement into several addons.
I don't want to add an other dependency for something best handled by a dedicated addon.

If someone has the motivation to implement it into weakauras maybe we can review a PR for this, it depend on the position about this from other devs.

ClassicThreatMeters and ElvUI seem to both use LibThreatClassic

I agree with Buds, if there's a PR, we can review it. Otherwise it's out of scope.

I see no point in keeping the ticket open, if no developer wants to work on it.

In my experience that will eventually just lead to a bug tracker full of "dead" tickets. If someone, not currently a developer, wants to work on such a trigger, the existance of the ticket won't make any difference anyway.