I am not sure it was designed as cross-application support? I mean, cingg can load both TOC types, so it works...
Are you concerned about more self-contained toc file for inter-application operability or self-documentability reasons?
How other apps (like Natron?) handle this?
Sorry, I don't understand what you're asking. I tried to do a dpx render; it came with all the images and a TOC file that doesn't have the links to the images. Then I created a second TOC file using imagelist.sh. A TOC came up with the links to the dpx images. This doesn't work when imported into CinGG; it's obvious because imagelist.sh uses only jpeg images and not dpx. So I took the first TOC and pasted in the links from the second TOC. This TOC+ works in CinGG and Natron; it doesn't work in Kdenlive and OpenShot (but I don't know if these programs support DPX). I redid these steps using PNG instead of DPX and the TOC+ works in CinGG; Natron; OpenShot but does not work in Kdenlive.