So far I’ve used delta chat only for chats and not for traditional mails, but with the android version 1.28.x I’ve started to use it with all the mails by checking only the delta chat folder and using the filters to automatically move some mails in the DeltaChat folder (this is a really useful feature, good job on the implementation).
To use at best DC as a client for all mails in my opinion we need two features:
the first and most important is the possibility to automatically delete from the server only the mails contained in the DeltaChat folder, in this way you could use the filters to move the mails that once read you want to delete, and keep on the server the mails received in the inbox.
The second would be the possibility to choose which folders to control besides DeltaChat. For example I already use filters to move newsletters in dedicated folders or other mails in other folders and I have no way to see them on DC.
Edit with some additional considerations on the first suggestion
Currently DC just installed works by default only with chats but when you open a chat you get the message that it doesn’t matter if the user to whom you write uses DC, this can be misleading because if the recipient responds to the mail it will be received by DC, but if the same contact who does not use DC starts another “chat” it will not be visible in DC and also if the recipient does not use DC or a client that uses autocrypt the messages will not be encrypted. I think it would be better to have the default option to use DC for all mails and automatically move the chats to the DC folder (meaning by chats the mails exchanged between DC users). The current risk of using DC with all mails is that if you decide to automatically delete mails from the server you will probably delete mails you don’t want to delete. While deleting only the mails moved to the DeltaChat folder you could manage in a more granular way the mails to be deleted automatically.