As one who's worked with numerous rookies who have the powerful Crossword Compiler at their fingertips, I can tell veterans not to worry about the creation of very large word lists, at least insofar as themed puzzles go. Why?:
1) The sine qua non of a themed puzzle is, quite obviously, the theme. Some beginners are very gifted at coming up with themes, but they're the exceptions. Some learn through mentoring and paying close attention to the themes of the puzzles they solve. Some will never get it. No computer will ever be able to generate quality themes.
2) Grid design has, imo, actually been hurt by the Crossword Compiler grid libraries. I keep advising students to learn to design their own grids, but many ignore me. The designs that work beautifully for one set of theme entries are almost never ideal for other themes. Plus, students invariably seem to select designs with low word counts. That just magnifies the problem. I honestly believe that those who refuse to learn how to design their own grids for themed puzzles will never make it to the big leagues. They may luck out once in a while and make a few sales, but, by and large, they'll be turning out inferior puzzles.
3) A problem related to both themes and grid design is the tendency to try to do too much with a theme. I've seen 15x15 theme proposals that I thought were for Sunday puzzles. Also, most beginners love the idea of adding short thematic extras. They have no idea how constraining this is when it comes to fill. Nor do they understand that editors are usually underwhelmed by short asymmetrical thematic extras.
4) Finally, running a manual autofill with Crossword Compiler by no means guarantees a quality fill. I don't see this changing with the advent of the best ranked word lists imaginable. If the grid design isn't optimal, the fill is likely to be poor. If newcomers fall in love with some fill entry or other and are determined to keep it no matter what, they tend to wink at some incredibly poor entries that are required to enable the entry that they're so infatuated with. To make matters worse, often those entries that doom the grid to failure are shorties. I've lost count of the number of times I've seen obscure or out-and-out unacceptable long fill entries so that the constructor can hold on to a 3- or 4-letter word with a Z, X, or J.
Coming up with a good fill, with or without Crossword Compiler, involves identifying the most constrained sector(s) of the fill and starting there to make sure one has acceptable alternatives. Most newcomers don't do this. If one starts with the easier sectors, gridlock is often inevitable. Then the constructor has to have the discipline to rip out the fill that was so lovingly created earlier and start over. Very few, in my experience, have that discipline.
Even with large, well-ranked lists, inevitably there are going to be some clunkers that work their way into a fill. Two tools that can be an enormous asset to the vet have, imo, really clouded the issue for rookies.
The first tool that gets misused all the time is the cruciverb data base. Students look up an entry, see it's been used once in the NYT, and go no further. I keep trying to preach that what Will will allow in a low-word-count themeless or a very complex themed grid, he'll reject otherwise. The rare usage of any entry has to be examined in context. Usually my advice seems to fall on deaf ears.
The second tool which can be more of a curse than a blessing in unexperienced hands is Google. There's a tendency with all of us to want to justify some obscure entry that saves our fills. Rookies will spend a lot of time using Google to try to convince themselves that some clunker is really a fine entry, and convince themselves they do.
I'm convinced that there's something I think of as "puzzle sense." For those who have it, particularly in the area of theme creation, Crossword Compiler will help them get to the promised land a lot faster than in days of yore. For those who don't have it, Crossword Compiler will only delay the inevitable "I quit," usually followed by "What do editors (and mentors) know anyway?" or "Who makes up these dumb rules?"
When it comes to themeless puzzles, I think Crossword Compiler has already raised the bar. I do believe that there are a lot of people turning out good themeless puzzles who wouldn't have been able to do so before the advent of Crossword Compiler. I'm not at all sure though that large intelligently-ranked word lists will have a big impact above and beyond what manual autofill and the cruciverb word lists have already had.
For wide-open Friday grids, often the key is to seed the puzzle with a pair of drop-dead-gorgeous entries and then design the grid from there. Crossword Compiler can't design grids.
The advent of good ranked word lists may let more novices into the Saturday game, but even there, I don't think any of the Saturday specialists need to lose sleep. The superstars will usually seed their Saturdays with entries, many of which are desirable precisely because they don't appear in any lists.
If the large ranked word lists become a reality, it will be interesting to see if there's a sense of sameness to the themeless puzzles being created. If that turns out to be the case, it's likely that the established superstars will shine all the more brightly. A very high ranking may be the kiss of death to some lively phrases that don't show up all that often at present.