I have something I've called a solera with lambic although it's not technically a solera because I'm only using one vessel. I think we've all adopted this same single vessel technique as a solera for beer terminology.
I'm using a six gallon better bottle. I have been running it since December 2010. Each December I pull out a portion and replace it with an equal amount of fresh wort. The first year I brewed a very basic and simple recipe with 60% pilsner malt and 40% red wheat malt, decoction mash and pitched the WY lambic blend plus the dregs of a Lindeman's Cuve Rene (the only non-pasteurized sour I could find at the time). In December 2011 I pulled four gallons, put one gallon aside in a separate jug, put one gallon on raspberries and aged it for six months before bottling, and bottled two gallons straight. The first refill I did the same recipe except I used white wheat malt and added a tablespoon of whole wheat flour near the end of the boil to add some starches into the wort. In December 2012 I pulled three gallons, bottled one gallon, put one gallon on blackberries which I will bottle in the next month or two, and put one gallon in reserve in a separate vessel. I replenished with three new gallons, this time using 60% pilsner malt, 40% unmalted wheat and a decoction mash. This coming December I am going to pull another three gallons and blend it with the separate gallons held back from year one and year two to make five gallons of gueuze. It will be a good time in my house next year.
I have definitely noticed a difference between the two bottlings. Year one has a big cherry flavor and the acidity is sharper than the second year. The second year is more funky and leathery with very soft acidity. Other than age and some differences in the wheat, I think the absence of esters from saccharomyces in the second year deprived the beer of the typical cherry pie flavor I saw in year one. This last December when I refilled I added a very fruity Belgian sacc strain to see if the presence of new esters will produce a lambic with more cherry pie flavor. Not that the second year's leathery flavor isn't good but it was a good opportunity to test a hypothesis. Plus having three unique tasting lambic should make for a more interesting blend this winter.
If you want to read more of my ramblings about the solera you can see just the solera posts on my blog on this page: http://homebrewingfun.blogspot.com/p/lambic-solera.html
I think the solera process naturally lends itself to sour brewing because the solera works off time and time is naturally a key ingredient in sour beer. The same is true for brett beers because brett does some really interesting stuff over time with flavor and a combination of fresh and old, brett'd beers could produce some really complex and interesting flavors you may not be able to produce out of a single beer aged with brett.
I can also see it making an interesting beer out of a stronger beer, whether it was a barleywine, a quad, a scotch ale, etc. and then bottled by itself each year or blended with a young beer in the package. I wonder how long a clean beer, even a bigger beer, could last before brett, pedio and other critters showed up and took up residence. Not that it would necessarily be a bad thing.
I think of the solera process in the same vein as blending but you are letting nature decide some of the flavor elements rather than developing all of the flavors through your blending process. There's still control over the grist, hops and to an extent the fermentation products but the maturation and melding of flavors over time in the solera is mostly out of your hands. I don't see that as an excuse to just throw whatever beer into the solera, you should think about each beer you add based upon how the flavors in that beer change over time and how they might blend into the solera and how it is going to change the overall flavors in the solera. It's easier to predict the change in flavor and ensure a positive change with a repeated addition of the same beer or a similar beer. You can always blend the solera beer with a disparate beer in bottling but once a beer goes into the solera you can't take back those flavors or how they will mature.