I agree with you, integrating a support for more archive formats in the base release doesn't take a lot of space and is useful.
It appears that the 7zip format can't be handled by Ark (why???). There is p7zip, the command line version of 7zip for Unix (supports 7z, ZIP, CAB, RAR, ARJ, GZIP, BZIP2, Z, TAR, CPIO, RPM and DEB, says the website).
Rar is non-free so can't be integrated in the base release (maybe we can make a .pbi). For ACE I don't know. But Zip and 7Zip are free formats, and at least .zip support should be included.