It would be a very important feature to be able to filter DNS requests and be able to block tracking domains.
I know that on android the ability to filter domains can already be achieved with very nice applications such as RethinkDNS but all these applications use a VPN connection and using it does not allow to connect to other VPNs which makes it, at least for me, not usable.
As an implementation I have in mind the possibility, typical of linux systems, to edit the /etc/hosts file and to redirect some sites to 127.0.0.1.