I like the thinking of ppl in this thread. A lot of these responses are pretty well thought out. But to answer your question: No one could possibly make a logical, educated guess, no matter how hard they tried or what data they use to justify their answers.
The trickiest thing about domains is their unpredictability. Some kinda of domain ie a LLL.com has an 'inherited' value, a minimum base that one considers to be the norm for the type. If you had a random LLL.com, for example, it's putative that the domain is worth at least around $3,500.
Was it foreseeable that they'd get to the $x,xxx mark? By most, no. This time 10 years ago, it wouldn't have been assumed to net the $8,000 they typically hovered around pre-Recession. I saw a thread here about 5 or so years ago that had a load of LLL.nets on sale for about $65 each. If the seller knew they'd have been worth so much today, I doubt he'd have sold them so cheap.
A few years ago, I saw a guy on eBay selling L-L.coms for ONE DOLLAR EACH! You read that right -- far under reg fee. Try getting one for reg fee now. I feel jaded like mad that I didn't buy the dozens he had for sale @ $1 each.
So you see, ten years is a long time to speculate on.
There are a few things you can keep in mind, however, that could give you an idea. There are more LLLL combination than there are LLL and thus there are more LLLL's in this world than LLL. Logic states that by sheer volume, there are many more valuable LLLL's than LLL's and the same for worthless LLLL's. This isn't to say there are higher-value LLLL's than LLL; I'm only speaking of the fact that there are more valuable LLLL's out there. Your definition of 'valuable' might differ from mine but I'm sure they're in he same vein: Yielding a high ROI.
There are 3 classes of letters: Premium, middle and anti-premium. Search the net if you want to verify this claim but the most used letters in English and the most sought-after:
A, B, C, D, E, F, G, H, I, L, M, N, O, P, R, S, T
Letters that are used less and are NOT premium but are considered decent:
J, K, U, V, W
And the anti-premium letters:
Q, X, Y, Z
If your domain has all premiums or 3 premiums and a 'middle' domain, it would more than likely be worth holding on to. OR if your domain is grammatically pronounceable (something that can be pronounced according to English grammar) or if it has a consonant/vowel pattern, then you have a keeper.
Good domains:
DERO.com (Grammatically pronounceable and CVCV and quad premium)
ARES.com (Grammatically pronounceable and quad premium)
APIL.com (Grammatically pronounceable and quad premium)
RECK.com(Grammatically pronounceable and triple premium plus a 'middle' premium)
Bad:
XEWQ.com (2 anti-premiums, 1 middle)
SEQL.com (Some might say it is pronounced like see-cool but grammatically, it doesn't)
There are many factors into it but if you have a good LLLL.com, then you should definitely hold it; otherwise, drop it. Again, looking at proportions, there are many LLLL's out there and the odds that they'll all be bought out and STAY bought out (like the LLL.com's) aren't good. But will there be a LLLL.com buyout that holds? You don't know. I don't. NOBODY knows. No one believed CCC.com's would ever be bought out but look at what happened. Domaining is a fickle thing, an art form in itself. We can't say what'll happen in 10 years' time. All we can do is speculate and see what happens. But it's best to play the safest cards unless you have a grand budget and are not afraid of a potentially massive loss.