I will definitely consider doing exactly that. I have sone smaller demijohn as well, 5 litres or so. Is it worth bulk aging vs bottling?
I may well bottle half (a friend invested in some so 5 bottles each approx) and then bulk age after adding cubes for 2 minths
I've found that bulk aging is very similar to bottle aging. I prefer bottle aging because:
K-Meta that you add to stop fermentation (along with the sorbates) also protects your mead against oxidation. K-Meta's purpose is to provide free SO2 in the solution, that keeps protecting from oxygen and other infections for as long as those numbers (PPM) stay up.
However, K-Meta is a volatile substance so eventually the SO2 breaks down, evaporates and "airs off" out of the mead. So, if you bulk age, by the time you want to bottle, chances are your SO2 levels are lower in number than where you pitched initially, so you're going to have to add more. And since I doubt you have a device to measure the free SO2, you're not going to know how much to add. Too little and you risk oxidizing your mead with the bottling process. Too much, and you risk having your mead taste of sulfur (rotten egg notes).
Now, if you bottle while your SO2 are at the correct levels (I usually add sulfites in two additions, one RIGHT at the start immediately after racking, and another right before backsweetening), you have less risk of this and you know you're bottling a stable product. Your mead can then rest in the bottle and develop without you worrying about bottling day.
I have found no difference in quality between meads that were aged in the bottle and meads that were aged in bulk.
Now the downside. Bottling has to be done properly and you have to fine the mead properly to ensure as little yeast sediment in the bottle as possible. Yeast in the bottle leads to autolysis of the yeast cells over time. Way back when I was just starting I didn't care for this much and didn't heed the warning. The result was a mead that smelled of rotten fish, purely due to a 1/4" layer of decaying yeast cells in the bottom of the bottle that stood there for over a year.
So what I do now is this:
1. After fermentation, I cold crash the mead. I leave it at near freezing for a few days, and then I add gelatin and bentonite to fine. I leave it on the gelatin and bentonite at near-freezing for at least another week. This is done to ensure first that most of the yeast drops out, and second to ensure the yeast cake (the lees) is nice and solid by the time I rack off it.
2. After the two weeks or so at near freezing, I'll sanitize a new container and measure out my K-meta and sorbates. There are calculators for this based on your mead's pH and ABV. Here I add the k-meta sparingly, bordering on the minimum addition. I add these to the new container, and rack the mead onto the chemicals. I leave it here (at room temp) for another week or so. This drops out a surprising amount of additional yeast and creates a new lees.
3. From here I prepare another container (usually my bottling bucket) - sterile again. I measure out another k-meta addition (to compensate for aeration and other stuff that might be there), add the backsweetening to the new container (be it honey or juice or Xylitol or whatever) and rack onto that. I leave it here for a day or so just to ensure everything is mixed properly and then I bottle. When I bottle here I know that the process is sterile, my SO2 levels are good and my mead can age in peace.
I tend to store a few bottles in random places around the house and then literally forget about them. I discovered a mead the other day I made 18 months before in a crate somewhere way in the back of a cupboard under the kitchen sink. I had forgotten what mead it was, and only remembered it was the one I backsweetened with apple and cranberry concentrate after tasting it. It was AMAZING. Crystal clear, full and rounded. It was amazing. Gotta do that again.