I honestly have little problem with sunburst as a concept. If anything, the main flaw with the mechanic was restricting itself to needing counters, which was basically fixed when it returned as converge (6 on the storm scale) in BFZ, a mechanic which would probably have been better received had it appeared in a set with a proper focus on it.
For example, in an environment in which most of your cards will be artifacts and there aren’t any multicolor cards, you shouldn’t expect to play off actual colors of permanents. This leaves us with having to use multiple colored mana somehow.
Again I think sunburst/converge are the perfect answer for this kind of dilemma. Simply make the effect play off the amount of different colors spent to play it and you’re done. As said before, sunburst’s real problem is that it limited itself to using counters, and if converge didn’t exist I would probably just make it and call it a day.
But converge does exist, so let us find another solution.
I gave myself the following restrictions:
The mechanic needs to use design technology existing during Fifth Dawn (so no ability words, keyword actions etc);
The mechanic needs to make sense in a world full of artifacts (so nothing that plays off the number of colors among your permanents);
The mechanic can’t do anything other keyword abilities in the block do (so no cost reduction, for example);
The mechanic should reach its maximum potential with five colors but shouldn’t need five colors to do anything.
So I give you infuse:
Sunforged Myr (C)
Artifact Creature – Myr
2/2
Infuse
(You may pay up to 
as an additional cost to cast this spell.)Sunforged Myr enters the battlefield with a +1/+1 counter on it for each color spent to infuse it.
Mirrodin's skies changed. Its surface soon followed. In short, when you cast Sunforged Myr, you can cast it for
,
,
,
,
and so on. For each additional mana you pay for it, the spell is infused once and you get one instance of the bonus effect.
Infuse is thus a blend of kicker, multikicker and converge. You can pay more to make the spell more powerful, you can do so multiple times, but each effect needs to be paid with a different color.
Flexible enough to go on plenty of other card types as well:
My submission is Sunforged Myr.
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,sacrifice cardname: search your library for a plains card and put it into the battlefield,shuffle your library ,then create a white 3\2 cat creature token, this ability has affinity for different basic land types.
: Add one mana of any color.
, but I'm not sure how 
