I saw the Reddit post briefly yesterday and saw some of the speculation but didn't go back and look to see if more info got filled in.
Just one ink would be a huge disappointment, sadly. It would have to be one heck of a Sailor pen to justify that price with just one pen and one ink, but they do tend to be expensive pens.
Seems unlikely there would be sufficient Pentel stuff I'd want to fill in the remaining gaps, but I'll wait for spoilers before dismissing it.