Renesas (Hitachi, Mitsubishi & later NEC) has nothing to worry about at least not for a while.
Atmel has been growing strong and surpassed Microchip in 2010 or so.
http://www.dataweek.co.za/article.aspx?pklarticleid=7412But not because of the maker community. Microchip went from way down the list to the top on the previous decade leaving Atmel, Zilog and others in the dust.
The funny thing about that article is that you gotta see Cypress (minus smartcards and automotive) growth of %139. Love their PSoC chips. And that is for MCUs it doesn't count USB chips. Then again Automotive is huge for sales, but it shows that Cypress is climbing up big time.
Edit: forgot to attach the picture, doesn't include smartcards and automotive mcus.

8bit mcus are pretty much at no growth but not loosing shares, 16 bits are declining and 32 bits are climbing (mobile stuff of course)
But 8 bit is going to always be king in price and battery life. All those cheap mp3/mp4 players have an 80C51 embedded in their multimedia chip, some PSoC chips have it too.
TI has been stale for a while but not loosing ground. Motorola?? well maybe they get royalties or something, Zilog, Toshiba, etc, might be getting royalties as well.
But even the lonely Z80 probably has shipped more chips than Arduinos and derivatives.
In any event, this was about an open letter, not about who can pee further away.
Myself I don't like the PIC branch instruction set (lack off) for anything lower than the PIC24 and they are very spartan as for the instruction set, but that implies less power consumption and longer battery life at a lower manufacturing cost.
Different strokes for different folks.