Within the sort of of communities where polyamory is popular, I don't think it will be a big problem for the mating market. There is some evidence that highly intelligent people are more androgynous. If so, then sex differences may be less sharp between intelligent people, which anecdotally makes sense. If intelligent people are less gender-differentiated in general, then perhaps their sexual preferences are more similar, too. If there are less sex differences in mating preferences, then there is probably less sex differences in selectiveness and less hypergamy.

In poly nerd communities, I don't know if there is a winner-take all situation for men, but it's hard to tell, since the gender ratio is so skewed. Let's imagine a community with 10 men and 2 women. Under monogamy, woman #2 dates man #10, and woman #1 dates man #9. What happens under polyamory? Do both women date man #10? Or do they both date men #9 and #10? Or #8, #9, and #10? Those all seem like plausible scenarios, and in the last case, there are actually less male losers than under monogamy. With a high male:female ratio, the women have their pick of 80+ percentile men.

Of course, outside this particular androgynous phenotype, the differences between monogamy and polyamory are likely to be more stark. Average people are already doing plenty of non-monogamous mating, so we can consider how well it's going for them.