Monotonicity of infimum of the Willmore energy with prescribed genus
As pointed out in the paper you reference, this question was posed on p. 446 of this paper
Kühnel, Wolfgang; Pinkall, Ulrich, On total mean curvatures, Q. J. Math., Oxf. II. Ser. 37, 437-447 (1986). ZBL0627.53044.
I found 19 papers citing this paper on Google scholar. Of these, one is a survey paper by Kuwert and Schätzle from 2012 which reproves the Kuwert-Li-Schäzle result (and doesn't mention the monotonicity question). A cursory look at the titles and abstracts indicates that this question doesn't seem to have been resolved (although there are several papers by Kuwert-Schäzle which address related questions). Presumably a paper proving monotonicity would cite their paper, so I'm guessing that this is still an open question since 1986.