Thanks @GuillaumeAV
Indeed with the ActivitPods architecture, it’s possible to have one POD account for many type of ActivityPub applications. It would not be difficult to write a small applications which post Notes understood by Mastodon.
I’ve come to realize recently that this architecture would be a way to go around a current limitation in ActivityPub: if you want to post messages, you must create an account on Mastodon. If you want to post videos, you must create an account on Peertube, etc. The diversity of applications is good, but the need to create multiple accounts is non-sense. With ActivityPods, it would be possible to have only one ActivityPub account (your POD) used by many different applications.