The T-34/0 keyboard layout by jonas_h features a repeater key.
Published on September 5, 2021 by KBD.news
The big change to the layout is the Repeat key. The concept is simple: when you press it you repeat the last pressed key – jonas_h.
I hadn't thought of that but this is an interesting concept.
Investigating the author's corpus, the Repeat could be useful, however, it does not qualify into the top 10 and so it does not outcompete Space or e as a thumb key or any frequent alphas of the home positions.
It's the 12th most frequent "letter" (without Space) so he would put it somewhere in the home box.