Well, to be a bit pedantic, it's not accurate to call this T1200. T1200 isn't a nomenclature standard, it's just the model name for a product made by Toray. The mechanical properties of this new Chinese product (dubbed SYT80) are about in-line with T1200 from Toray, so it would be more correct to call this T1200 grade/equivalent.
The most base logic behind Toray's naming convention is: letter to denote the mechanical property the product prioritises (T-tensile strength, M-tensile modulus), followed by a number roughly corresponding to the measurable value of that property (can be very inexact). There is often another modifier letter after that, denoting further specialisations (H, G, S, X, J, etc.) but that's less important.
Examples:
T800H: focused on strength, tensile strength measured at 796 ksi
M40J: focused on stiffness, tensile modulus measured 377 GPa
Now T1200 isn't actually any stiffer than T1100. Toray lists T1200 tensile modulus at 1 MPa lower than T1100. So they will both stretch a similar amount under the same forces, but T1200 is able to withstand higher forces before breaking. Their density is also about the same, so replacing the T1100 in a frame with T1200 won't make a stiffer or lighter frame. The only time bike frames are actually stressed to the point of breaking is during impacts, like crashes. That is when fibres experience loads out of their orientation, so the difference in their mechanical properties matters much less, and volume of material and mechanical properties of the resin are the main deciders of the result.
So on paper, I don't see much advantage of T1200 grade of fibres over T1100, for bike frames. That is before taking into account things that don't show up on spec sheets, like yields (main driver behind costs), production consistency, workability, etc.
