I think this is a really bad idea. There is a huge difference between a bicycle rental place and one that rents clothes. OSM in general has worked better with specific tags than with a generic tag and additional tags to identify what the place actually is. One reason is that it's easier for mappers to guess what the tag might be; the second is that using generic tags imposes a large burden on data consumers who now have to filter out lots of stuff which is not of interest to them when previously they could just collect a specific tag. Additionally it goes against the major precedents: car rental & bicycle rental.
I am not against separating product and service business within the shop key (in fact I suggested just such a set of categories 5 years ago), but shop=rental, like shop=trade is too generic. SK53 (talk) 14:35, 19 June 2017 (UTC)