As a libertarian anything that increases the ability of a 3rd party go gain traction interest me but something smells very off about the recent uptick in discussion of alternatives. If these changes were actually beneficial to the underdog in the general case you'd see them being pushed by the left or the right on a state by state basis depending on the political make up of any given state. The parties aren't run by…
I personally don't really care about the political impetus behind changing the election format (not to say I don't care about politics, just that in the case of alternative voting systems the standard US format is almost the worst you could do). Anything that moves the US toward something better would be an improvement.
My one concern is that for whatever reason ranking systems seem to be the thing being pushed most, when approval or rating systems would probably be better.
Changing to an approval system would probably be the easiest way to increase 3rd party viability at the moment. Which of those 3rd parties would benefit is a different issue, but approval systems allow people to diversify their expressed preferences, so at the very least it wouldn't be worse for 3rd party candidates.
The basic issue is that plurality voting is a very poor measure of preference. Imagine if you were asked to measure height of 5 people in the room, 3 of whom are over 6 feet 10 inches tall. You could report how tall they are; this is most similar to a rating system. You could rank order their heights; this preserves rank ordering information but not anything about absolute difference, so the two people who are 7'2" and 7'1" look as different as the people who are 7'2" and 5'2". You could also ask people to just mark which are taller than 6'10", which at least acknowledges that more than one person could be taller than 6'10", and preserves some info about absolute height. Or, you could do as is standard, and just indicate who is tallest, which doesn't preserve much information at all about height.