What kind of feature are you missing? Where do you notice a shortcoming of PTB?

Bot API 7.2 added the parameter business_connection_id to all the send_* methods.
I imagine that if a business wants to connect a bot to its business account, that often times it will have a custom-build bot for that such that the bot will only ever see one fixed business connection. Moreover, the bot would only ever do communication via the business connection.
For such use cases it would be benefitial if one could set a default value for the business_connection_id parameter via PTBs Defaults mechanism.

Describe the solution you'd like

Add Defaults.business_connection_id and make the necessary adaptions in ExtBot code.

Describe alternatives you've considered

If Message.reply_* already passes business_connection_id as discussed in #4180 (comment), that may already cover many of the use cases. So Defaults.business_connection_id might not be completely crucial.

Additional context

I would see this as minor priority (+0), especially since the functionality is very new and we don't know yet how many people will actually be using this. If someone would like to PR for this, they are welcome to, but I personally wouldn't put any effort into this from the PTB team in the forseeable future.