Each recurring Mario character that has been around since the Nintendo 64 days has a very distinct voice as of today , so as i said before , changing that at this point would only ruin the character in my opinion. Not only that , if any of these people were to be ''replaced'' , they would most likely hire a sound alike voice actor , which again makes it useless to replace the originals.
Again the case of Peach, Jen Taylor voiced Peach with a very distinct voice since 1999. Her performance didn't exactly sounded a tad similar to Asako Kozuki or Leslie Swan , the gals that previously voiced Peach.
Since Jen sticked for several Years , Princess Peach voice became so iconic and spottable that when Jen was replaced they needed to hire a ''sound alike'' , which was Nicole Mills.
After that , they hired another , and this time 100% Perfect sound alike , which is Sam Kelly , who adds even more personality to Peach other than your cute pink blonde princess , most noticeably in Smash.
So , again , replacing these people would only mean that we will get a sound alike actor or actress.
Lastly , as for Rosalina , there's not much to ''fix'' as Laura F. Smith can easily provide a very good performance just by lowering her voice, i don't think she needs to get replaced , though if she ever was , i would love somebody mainstream or not , that aleast has a lower pitched voice , because Rosalina sounding all girly out of the blue is a big no for me