While i can see a benefit in such a service ... anyway, one (and a half) questions out of principle:
Are you actively participating in Lemmy or the "Fediverse" at large, meaning that you'd have a vital interest in the development of collectively-operated social networks?
Or is it more so that you jumped on the opportunity to perhaps be the first company to put an advertisement in people's feeds, in order to make a buseness?
... I may add, this is advertising a service which potentially would allow for customer lock-in, and at the same time it would allow the service provider to potentially gain power over parts of the network. Lemmy instance admins would in essence hand their keys and trustworthyness to a third party. That is concerning.
And ... this is calling for a feature request: advertisement flag, including an ignore option in user settings.