Debian's Apt 1.9 Moves To Experimental, Coming To Ubuntu 19.10
The Apt 1.9 packaging system is a big update that does include API/ABI breakage, including necessary changes to the Python and Perl interfaces. Apt 1.9 is working towards an eventual Apt 2.0 release, but for now Apt 1.9 is what's being targeted by Ubuntu 19.10 and will be available via Debian experimental.
One new command to Apt 1.9 is the apt satisfy command that can be fed build-depends strings to specify the needed dependencies and then Apt is responsible for figuring it out and installing those dependencies.
More details on the Apt 1.9 experimental changes at this point can be found via this Git commit.
Apt 1.9 experimental is now in the process of landing in Ubuntu 19.10's archive.