Extending lifespan/updates for themes

not sure if this suggestion has been made before, but I just posted this in the comments thread of a theme I purchased a while ago:

Same here – really disappointed with several promises over the last few months that an update is “imminent”… seems like empty promises and tactics to keep sales going for a little longer. To make a constructive suggestion: In cases like this (e.g. themes older than 5 years) I would be willing to pay for an update to a new theme version (e.g. half the original theme price).

If this helps to keep authors motivated and able to continue updating themes that have sold well I think quite a few customers might be willing to pay for an update. This should not evolve into a “membership model” with monthly fees but I think it’s appropriate for current average life spans of themes to limit the initial update period to 3 or 5 years and then offer a paid update (which should include more than just bug fixes and compatibility updates).

Any thoughts on this?