I do not know yet. In the long run, if Sigma will offer a 28/2.0 i-series, I will very likely prefer that.
But that also depends on the next L-Mount body. I still hope for a smaller, rangefinder style body.
My S5 II is in many situations too big for me. The Ricoh GR3 is a great alternative, but I would love to have additionally something with a viewfinder. Just to be on the safe side, if the sun is too strong.
For my Fuji XPro2 there is the 18/1.4 available. Very good lens, but big. For the optical viewfinder too big and the old XF18/2.0 is not good enough (image quality).
A Leica Q3 as an alternative is not high on my list, because of price, too many pixel (even with pixelbinning you have only the options for 60/34/19, but not 24MP), and the name, which is in some areas attracting the wrong people.
As you can see, there is really a niche, if you want to have a small 28mm AF lens. Not only with L-Mount.
MFT has a solution with the Leica 15/1.7 lens. Great lens by the way. The GX9 is the perfect fit for it. I just wish they would bring out a GX10 with a modern 24MP sensor and a better viewfinder.
This all sounds like a spoiled kid. But if the different brands would research in the same way, they would find out easier what to produce next to increase sales. If someone is new, wants to decide for a new camera system and his preferred focal length is 28mm, these thoughts will influence in which system he will invest.
L-Mount is in a very good position thanks to the i-series lenses. But Fuji for example has a problem. Each new lens is just getting bigger and heavier. That was not the DNA with which Fuji started for the X-system.
Also Nikon has a problem. Nikon's lens mount is too big. Therefore all lenses will be bigger than the counterpart of other brands. Additionaly, there is because of the big lens mount with small bodies (i.e. Nikon Fc) not enough space on the right side to comfortably hold the camera. These were the 2 main reasons why I sold my Nikon Z systems.
Canon R is not an option for me for various reasons.
I had a Sony A850 and Zeiss lenses a couple of years ago, but after their back and fourth in the different mounts, there was no trust anymore to justify a long term investment and I sold it.
Pentax would be interesting, if they would bring out a small fullframe DSLR (they never will bring out a MLU IMHO).
But I digress from the topic.
LMount is IMHO the best system to be for fullframe. If you do not need/want FF, then MFT is the choice of my heart.