This is nuts. I don't see a big change it wouldn't make sense
I can't ever see Siemens changing their STL or at least not providing a backwards compatibility mode. There is way too much code written for STL to ever drop it.
The problem I see is that when the S7 was developed the CPU was probably fine. However, it is going to be a bottle neck in the future. The S7 CPU really doesn't handle higher level languages very well. The S7 CPU can be made faster with technology but the basic instruction set and architecture is getting old.
Instruction list is much different from STL but similar in that it is almost like assembly language. There is a couple SIGNIFICANT differences between STL and IL. IL assumes the CPU is an ideal stack machine and there are no registers. When writing code for STL you must get into the registers. This limits future growth because you can't change the registers unless you simply add more registers to what is already there. In IL there are no registers. The CPU is virtual so one can simply port the IL code to a faster CPU.
I think the way out is to support STL and IL and to support both the old STL CPU and whatever comes next. Modicon did something like this where one can run the old 984 ladder or the newer concept software and firmware.
