I don't keep track of Mac stuff but I thought that was just for the app store.

The official version of DOSBox isn't supported in any app store so it's not a problem.

Future versions of MacOS will supposedly drop 32bit support. Seems like that would be a good time to drop MacOS if so, imo.

1st it‘s not true that High Sierra drops 32bit support, there might be a hurdle or a warning displayed, though.
2nd it‘s easy to compile a 64bit build of DOSBox (actually easier than building a 32bit build) but it doesn’t make sense as that is very much slower than a 32bit build on OS X.
3rd High Sierra will not be released before next tuesday and I‘m reluctant to update since submitting apps to the app store can sometimes be problematic if you do it from a beta MacOS.

Thanks DosFreak and Dominus. I did wonder whether it might just be App Store support they meant, and I agree about Beta so was reluctant to try it myself. I may well set up a test disk to try it myself next week.... and will report back.... watch this space....

As promised, I have built a new MacOS disk and tested DosBox and it works fine for me in MacOS High Sierra Beta.
I first built Sierra onto a new disk, loaded DosBox 0.74-1 and set up my DOS program which was an old Dos Banking program I bought in 1992 called Page Cheque Book (PCB)..... I then upgraded to MacOS High Sierra Beta and tested PCB again ... it all worked just the same.
Note: I have not tested a new installation of PCB on MacOS High Sierra Beta but would assume there would be no difference....
Hope this helps....

thanks, I can also confirm that it runs fine on High Sierra, both the 0.74-1 and SVN built by me.