Legend of Legaia used a similar battle system for its game, where directional inputs lead to special attacks, and the special attack itself counted as an input for another.
https://www.youtube.com/watch?v=GJfQl0Qr3hg
High Low High = Somersault. The Somersault triggers on the last 'High' and that still counted as input for another skill.
High Low High Low Low= High Kick, Low Kick, Somersault, Low Kick, Some other skill I forgot the name of (IIRC, the special attacks had to be different to chain this way)
Legend of Legaia utilized a system similar to old fashioned TP where it's built and spent, where as 2.0+ TP functioned more like standard MMO "Energy" systems, as well as maximum number of inputs per turn.
Current FF14 has no TP system and no 'maximum input', other than building a limitation into Monk itself.
Building it into the Chakra system would serve as a suitable limiter. Basic weaponskills build Chakra + inputs for the special ability, special ability spends chakra. Weaponskills falling into a category with a gauge representing your last 3 inputs / skill type.
So every special attack could have a 3 input string, while varying chakra costs.
So you have things like Dots, Buffs, Debuffs being lower cost chakra with big finishers being higher chakra costs. The goal is to minimize your Input strings to get the right special finisher with the appropriate chakra to use it.