Why? The 12-50 is a great, feature-rich lens for what it offers. I picked up a new one for $99 some years ago. It's always on my primary body.
As for the $99 40-+150r, I couldn't get rid of that fast enough. I'd suggest the Panasonic 45-200 Mega instead, if you can't afford anything higher up the price chain. I remember using that lens and regretting my m43 purchase, until I bought the 12-40 Pro.
The 75-300 is a good lens. Probably the best m43 lens value (FL vs price vs image quality). I'm glad to see the Olympus 100-400 making other super telephoto lenses more affordable.
Why not have an option for the customers? Olympus 12-50mm is the cheapest weather-sealed lens, it's not the best lens out there but it's not priced like the Pro line. Currently if you wish/want/need weather sealing on telephoto you have:
*Olympus 7-14mm f 2.8 Pro: 1150 $
*Olympus 12-40mm f 2.8 Pro: 1000 $
*Olympus 12-45mm f 4 Pro: 650 $
*Olympus 12-50mm f 3.5-6.3 EZ: Used 100-200 $ (because it was discontinued)
*Olympus 12-100mm f 4: 1300 $
*Olympus 14-150mm f 4-5.6 II: 450 $
*Olympus 40-150mm f 2.8 Pro: 1350 $
*Olympus 100-400mm f 5-6.3: 1500 $
*Olympus 150-400mm f 4.5 Pro IS 1.25x TC: 7000 $
Making it ONE option under 250 $ and TWO Options under 500 $, of which only one goes past 50mm. If you are willing to go with Panasonic you have these options:
*Panasonic Leica 8-18mm f 2.8-4: 1100 $
*Panasonic Leica 10-25mm f 1.7: 1800 $
*Panasonic X 12-35mm f 2.8: Mark I - 700 $, Mark II - 1000 $
*Panasonic Leica 12-60mm f 2.8-4: 1000 $
*Panasonic G 12-60mm f 3.5-5.6: 500 $
*Panasonic G 14-140mm f 3.5-5.6 Mark III:
*Panasonic X 35-100mm f 2.8: Mark I - 900 $, Mark II - 1100 $
*Panasonic G 45-200mm f 4-5.6 Mark II: 450 $
*Panasonic G 100-300mm f 4-5.6 Mark II: 650 $
*Panasonic Leica 100-400mm f 4-6.3: 1700 $
So there are no options under 250 $, and 2 at 500 $ (though they are not internal zooms).
One of the big benefits of internal zooms is for video recording and usage with waterproof housing, among other things.
There are people out there where every $ counts and there are limits to how much they can spend even with savings, I think an internal zoom and focusing, weather-sealed 50-200/250mm f 4-5.6/6.3 that is light and compact (like Panasonic X 45-175mm f 4-5.6) .... and, if possible, make it under 350 £.
Sell it as a dual kit option for E-M5 II/III. Sure you have the 12-40mm f 2.8 Pro and 40-150mm f 2.8 Pro which adds up to about 3500 $, then there's 12-45mm f 4 Pro and (possibly) 50-200mm f 4 Pro for (maybe) around 2.500 $ and then you could have 12-50mm f 3.5-6.3 EZ and 50-200(250)mm f 4(4.5)-5.6(6.3) EZ for around 1.500 $ (if they E-M5 III is 1000 $ for the body).