The roleplaying game's skills will have a general skill or skill group. This will represent the collapsed skill that can be used when you are using it for general stuff or when the game isn't allowing for that skill to explode. Some games will just not need all your skills to explode open for a greater level of detail. I seriously doubt knowledge type skills will require more detail for example. But you can also have two games that are played with different focus. Lets say shadowrun is the setting, one game may not focus on decking, so no exploding of matrix skills. The second game is all decking all the time so it almost requires it.
As I currently see it skills would have a list of sub skills and talents. These would be purchased to round out a skill branch. Your skill would directly transfer over to some primary subskill you selected. Then you reduce the skill pay four points for your next sub skill or talent. Talents would only be available if you already have that same number of subskills. If you have one subskill you can have one talent. Once you have a number that can not be positively subtracted by four you are done.
For example a stealth skill of 2s3 that is unexploded may work like the following. 2s3 hiding sub skill. Then you subtract four for 1s7 in sneaking. Next we want a couple of talents again subtracting 4 we have an effective 1s3 and talk a talent that allows for faster sneaking. Our second talent drops us to effectively 0s7, we take a sniping talent that allows for hiding successes to be added to attacks. We may want another talent but can only have as many as we have skills. Her were would need another skill at 0s3 for tailing. We are done here as we cant go negative.
You will notice in the above example its actually best to take our three skills and then our talents. As that would make our tailing at 1s3. I think the way this will work out is you will take the skill or talent at the time it becomes available then as you increase skills it will automatically increase the whole tree. That way you are again losing out if you don't take your skills early in your progression but you will also not have the advantage of the talents.