Are you offering?
I've not gone through the pros and cons of Nextcloud vs Synology's various packages. Someone want to do it?
one thing is that nextcloud is opensource and using federation you can easily build a "bridge" between the files you share in public with the your own nas. Also you have a lot of apps usable on netxcloud, for example you can use libreoffice onlineeasily and such things.
I will need to understand how an app work on synology but it seems feasible . Owncloud can be installed manually also : Install Owncloud 10 on DSM 6.1