I use gamma 2.4 timeline with output gamma set to same as timeline.
Probably doesn't make a lot of difference. My assumption is our stock video footage will be used in a larger project whose final output's gamma is set to whatever they need/want.
Thats my working assumption. Unlikely most other video work, in the case of stock you really dont know what the final output format will be. Could be anything from web to mobile device to broadcast or cinema.
My only possible thought is the stock websites by default that buyers will see are generally displaying in 2.2 or similar so the previews and thumbnails if set as 2.4 are going to look too bright and maybe washed out. But again that assumes the site reads and uses the tags correctly to generate those previews.
Still open to any other suggestions but so far "makes no difference" is my working assumption.