Will Apple's solution be limited to Safari? I would think Marco's customers are rather a tech-savvy crowd who wouldn't tie themselves to just one particular browser.

I use Instapaper for the multi-browser support (mostly in Firefox), but also for the Kindle support, both for reading in Kindle Webkit browser and as downloads.

I think Marco has a big chance to catch the long tail of read-later'ing.

If you look at desktop Safari's Reader Mode… It is a fantastic feature but I don't think I ever heard of anyone I know using it.

It should've been implemented in iOS Safari long time ago, btw, this is where it's been missing.