if 35m lenses get the size of medium format lenses (or S lenses) -and the 2490 does imo- then one big advantage of 35mm (or called ff today) is gone. I thought mirrorless and evf were a chance to reduce lens size, but Leica seems to habe a different approach.
(bolded) I can't help but believe that is a mistaken notion. Just look at the *only other* FF mirrorless system out there (the Sony A7 series) and its lenses. There are only a couple of those lenses that are "small", and they're relatively slow and modest focal lengths. The fact is that fast lenses which cover a 35mm FF format properly tend to be a bit larger than small, and the optical designs to optimize them for digital sensors generally put them into the same size class as top quality lenses designed for SLRs and FF digital sensors.
Look at the Fuji X system lenses, too. They're designed for an APS-C sensor, yet they're not particularly small. Micro-FourThirds system lenses can be quite small, on a quarter size sensor format, but the fast, pro-quality lenses even there tend to grow in size quite a bit.
The major advantages of 'mirrorless' and EVF are really a short mount register, making room for better optimized lens designs for a digital capture sensor (regardless of size), the removal of the mechanical reflex mirror mechanism for lower vibration and again more lens design versatility, and the promise of a suitably high resolution, high performance EVF to out-perform an optical reflex viewfinder in terms of features and tools. I think with the latest generation of EVFs (Olympus OM-D series, Fuji X-T1, Sony Alpha, and now Leica SL) that promise is being fulfilled and the other advantages have been there from the first 'mirrorless' introduced, the Panasonic G1.
.. but why are T lenses smaller than comparable dx slr lenses and then the SL are biggee than comparable SLR lenses, nearly as bis as S lenses?
the size of the body is perfect for my taste
Most DX SLR lenses are derivative of 35mm FF designs and don't benefit much from the smaller sensor in overall size. The T lenses are being designed from scratch specifically for a compact camera system and are showing some size benefits from that ... but also notice that they are not*all ultra-fast and the focal length range is relatively limited as yet:
APO Macro-Emarit-TL 60mm f2.8 ASPH
Summilux-TL 35mm f1.4 ASPH
APO Vario-Elmar-T 55–135mm f3.5–4.5 ASPH
Super-Vario-Elmar-T 11–23mm f3.5–4.5 ASPH
Summicron-T 23mm f2 ASPH
Vario-Elmar-T 18–56mm f3.5–5.6 ASPH
Only the 23mm is truly small in that set, the others are middling sized (for scale, remember that the flange diameter they mount on is 50mm diameter). When a 18-56/2.8-4 appears, if it ever does, the equivalent of the SL's 24-90 for DX format, I would not be surprised to see that it was quite large.
G