It would be possible to do everything you are asking about and still stay within the Standard as long as the tail is below the horizontal, has the nice fanning spread, and the top line stays one complete line. It won't be easy though. If you get the tail too long with too short of legs, when the tail hits the ground, it makes a hump, which ruins the top line. Some of the modern US strains of Sumatras have the multiple feathering trait, which no Cubalaya I know of has. Multiple feathering makes more feathers in the tail, so you get a fuller, richer, tail. Some strains of Cubalayas have fuller tails with broader, longer tail feathers than do others. Cubalayas are not a true long tailed breed, they look like it because of the tail shape and angle. Do some strains need fuller, longer tails? Yes, absolutlely. However, making the tails into true long tail territory in my opinion is moving away from both the standard, and what the breed is, was, and is meant to be. There are lots of lovely true breed longtails around, so I'd sooner see people just keep some of them rather than make Cubas into longtails. I had some project "Cubas" gifted to me with very small percentage phoenix blood less than 12% for sure, and they still showed very long beaks, white ears, and pinched tails, and were very very flighty. They did have lovely long full tails, but the rest needs some work still!!
As for getting the leg length better, and the stance--Yes, both need improvement in many strains. That's an easy fix though, cross in a Shamo or Thai or Malay, and you will get the longer legs and more upright stance immediately. It will however take a while to remake the tails again, but the legs and the stance of the larger orientals tends to dominate for a long while. The real problem with what you want is that by using say a shamo you will get your stance and longer legs, but shorten and pinch the tails, and change the feather width and texture, for several generations. If you use a true longtail, you will mess up pretty much everything for many many many years, but get a beautiful , long full tail. Now, if we only had some Minohiki here in the USA, you would really be in business, but, alas, we are not so fortunate.
So, what you want is possible. It would be hard and take a long time. Adding longer legs and a more upright stance is in keeping with the standard more than making tails as full as what you have pictured. They should not be as upright as a shamo though, or as leggy, just in some cases more than they are now. Some strains could stand fuller tails, but, it may be better to get that from another strain of cubalaya rather than a longtail breed.
