A couple ideas:
Since they are so new there's probably not a lot of sand splash into the grass faces. Over time this will smooth them out and firm them up, kinda like topdressing. Similarly, it will become a less fertile growing environment. Older grass faces become harder and harder to grow grass as the sand buildup and pitch makes it very hard to hold on to nutrients and water. So that will thin it out a bit, but also invites weed pressure. Also, no one likes to sit around and wait for sand to build up.
The questions about irrigation and grass species are good ones, so I'll reiterate: Are there pop up irrigation zones around the bunkers? What grass species? Something like a fine fescue would work really good and would get happier with the sand splash, Kentucky bluegrass can grow thick and unruly if it's rainy or overfertilized or overwatered, and get progressively less happy with splash.
As for mowing, a flymower or hover mower works the best, string trimmers also work ok. I've heard of guys applying PGRs (plant growth regulators such as Primo) to bunker faces to knock them back a little.
All those issues aside, I would prefer grass faces to high flashed faces, which are an unholy time waster.
Tom,
I often recommend growth regulators and am surprised at how many times superintendents balk due to the cost of Primo (although there are some similar generics available to do the same work.) I would estimate that the labor cost would be saved, even at hundreds of dollars per gallon, but I haven't really done the math.
Of course, the design can help by tweaking the shapes to available mowers for bunker banks.
I would also think that a gently flashed sand might be more practical now that bunker liners are common. At least, I have been rethinking my bunkers in terms of making them work the best with liners. That takes both a good bunker liner and not much water draining over the top of the bunker to create a wash. Depending on the sand particle shapes (i.e., angular vs. round) those slopes that limit washing seem to be 25% or less. I know Better Billy Bunker recommends a maximum slope of 80% of angle of repose, but I have found you should really flash bunkers less than that. With some of our local sands, it seems like 15-16% is about the max to avoid repeated washouts. Sometimes, I will try to make the last few feet of the bunker up to 30% to keep the ball from lodging against the lip.
There are some design philosophy questions to answer as well. Good players often hate flash bunkers because a semi buried or buried lie in the slope near the green is punished more than a miss further away, but hitting the bottom of the bunker. That offends their proportionality mindset. I note the PGA Tour set up calls for tightly mowed bunker banks in most cases, to best assure shots don't get caught up in the banks.
Architects usually like the MacKenzie style because it looks good, even most of the player architects, but they often recommend less sand on the faces and other measures to keep them firm, and send the ball to the bottom of the bunker no matter where it hits. I have seen some of those Arkansas white sands where they really only have to rake the low point of the bunker because they get so firm, every ball ends up there.
Off topic, but the I am surprised there isn't more talk about the rugged edge bunkers being similarly "unfair" or at least, not proportionally designed.
I always thought Finger-Dye-Span did a nice job of building slightly flashed, visible bunkers that minimized washouts.