This is just plain silly.
Affinity Publisher is doomed if it does not at least support a flawless import/export of .idml files.
If you want to be a serious player in the graphic industry, you just can't ignore the biggest player in the market.
There will be at least a long transistion time before Publisher will be picked up.
Dig a bit deeper in the history of InDesign and you'll know why.
At the time InDesign was introduced, QuarkXpress was the industry standard.
Yes, Adobe was well known, but their former layout application(FrameWork) was mediocre at best.
It took Adobe a lot of effort and many years and tricks to get users to use InDesign.
Adobe was in a waaaay better position to achieve this then Affinity is now and here's why:
Quark had been ignoring user's needs for years and were very arrogant towards them.
Apple forced it's users towards OSX, which wasn't compatible with OS 9 at all.
There was a crappy transition period, but in the end every application needed to be replaced anyway
QuarkXpress was extrmely late introducing their first version compatible with OSX (v5).
They didn't even bother to add significant new features.
They did bother to charge the full update price, which was very high at the time (say, the prce of the entire Creative Suite)
Adobe did have a good reputation and allready Illustrator and Photoshop were the industry standards.
Well.... there was heavy competition for Illustrator, namely Freehand, which Adobe took over
InDesign was added tot the Creative Suit without any additional cost.
As allmost every company in the graphic industry allready used Ps and Ill, it was technically a freeby.
Remember ... it took QuarkXpress a few years to release it's first version for OSX (5.0) and it bugged like hell until 5.1.x came to market.
For which they charged another huge amount of money.
Still... it took Adobe 4 versions of InDesign (CS2) to overthrow the former reign QuarkXpress.
At the time, InDesign CS2 was in allmost every part of it superior to QuarkXpress.
Oh and you know what .... InDesign CS 2 was the first version with a flawless import of QuarkXpress documents.
Not a coïncidence.
Please don't make the same mistake as Adobe and support .idml (and .indd) as soon and as flawless as possible.
This is essential for success.
Btw, the ability to open pdf-files is need, but this is also far from flawless.
Even if it was perfect, you'd still be missing paragraph, character and object styles chained textframes, layout pages etc.