- More content for the next major DLC, whatever it might be (so long as its a historically based DLC), in general.
Their efforts may be restricted by a game design decision or something else, that prevents (or prevented) them from developing anything for one of the other DLCs currently in development.
- More effort on the Greek portraits, get them out before the end of the year.
The issue may be more complex than just an artistic solution. We don't know that, but given its delay, I betting there is more to it than meets the eye.
- More cultural portraits for underrepresented nationalities; Cumans, Turks, Persians (Middle-easterners are not as homogenous as the game represents), or more variety for the Europeans.
That sounds like a pretty big DLC, for so many nationalities. The Aztec portraits are probably rather simple and they only needed to create one.
- More diversity in unit sprites.
Again, sounds pretty big. And especially (in both's regard, actually), if they were limiting their efforts, there would be an outcry as to why they picked A but not B. But still, bigger than an Aztec Invasion DLC.
- More religious events, particularly with the new Pentarchy/Patriarch system. Possibly different ways to mend the schism.
Mending the schism might actually be a game mechanic aspect. And - like Paradox have stated - the Legacy of Rome DLC focused on the Eastern Roman Empire, and thus only allowed
them to mend the schism. But as you will recall, that decision can only happen based on a new mechanic introduced in that DLC/patch. Surely we need a similar expansion of game mechanics for Catholics to make mending the schism there interesting.
Like what? And there probably will be, but these seems to be things designed by game designers, not by scripters and artists.
- More 'personal' decisions, along the lines of feasts, hunts, and tournaments. Or more detail to them.
Hardly the work necessary for a DLC. And for what it's worth, can't modders do that as well? A DLC should - at the very least - be just above what a mod can. And if it is only what a mod can, then it should be more polished at least.
There's literally countless small improvements that could be bundled together with 1.08 to make a DLC that is both historical, just as not taxing on P'dox resources as this DLC was, and still worth paying $5 for. The ones listed above are just off the top of my head.
How do you know this DLC was taxing? For all I know, this was part of an experiment to test certain process and features out, by making a DLC like this. The result was deemed good enough to be released. Legacy of Rome was released like two weeks ago, and this DLC idea came about around that time; how is two weeks 'taxing'? And that's assuming it was intense work; but I have no reason to believe it was.