The main problem with this is that it makes it cumbersome to send notifications to the people you're thanking. I also feel like your method would come off as more impersonal, distant, and artificial.

I haven't gotten the sense that thanking donors is a huge problem, since funding drives only occur once a year. Perhaps if we had hundreds of donors rather than a few dozen leaving comments. I may be undervaluing the cleanness of the Recent Comments section because I don't use it regularly enough, but my current feeling is that a few minutes of annoyance for Recent Comments browsers is worth it for making an important comment section feel slightly more warm and personable to a much larger and less LW-savvy audience. And for giving Anna and Luke a bit less work.