The Future is Cortex M, you should sooner learn them,you have about 4000 different MCU's from different vendors, now compare your options with PIC The top players in this filed are ST(about 1000 devices) , NXP (600 devices) ,Cypress(450 Devices), Nuvoton(400 devices) and silicon labs(400 devices) ,Texas instrument (350 Devices)... and so on, and do not forget you have RF enabled ones like Nordic semi too
There's no doubt that ARM and Cortex M/A is the present, and the near future ... but I think it's worth keeping an eye on RISC-V as it's getting quite a bit of support from big names as it moves out of academia into industry.
- free and open license-free instruction set, similar in spirit to an improved MIPS. Inherently supports 32, 64, or 128 bit implementations. All standard instructions are 32 bits long, with optional standard Thumb2-like extension with 16 bit instructions duplicating the most common 32 bit instructions (gives ~30% code size reduction). Instruction set is designed for customization with plenty of room for vendors to add 16 bit, 32 bit, or longer instructions.
- supported by gcc, binutils, glibc, newlib, linux kernel, qemu
- Berkeley university has released three free and open core designs, roughly at Cortex M0+ (Z-scale), Cortex A5/A53 (Rocket), and Cortex A15/A72 (BOOM) complexity/performance levels. In fact they are all implemented as core generators, rather than fixed cores, with many aspects configurable (and they all share much of the same definition code).
- anyone can use Berkeley's cores or core generators, customized or not, or design their own from-scratch cores. This is in contrast to ARM, where Apple, Samsung, Qualcomm and a handfull of others have paid big big bucks to ARM to be allowed to design their own cores, but everyone else has to use off-the-shelf cores that ARM designed.
- roughly 40 companies are known to be working on CPUs and SoCs using RISC-V.
- SiFive, a startup founded by Berkeley people who designed RISC-V, have a 32-bit no MMU no FP microcontroller SoC that runs anywhere between 16 and 320 MHz in production. At the moment you can only buy it on their "HiFive1" Arduino-compatable development board. Later this year they expect to have a linux-capable quad core 1.6 GHz SoC and dev board. Their main business plan is to design and fab custom SoCs. They say they can add your peripherals, special function units, custom instructions, and get you the first wafer of sample chips for typically under US$100k.
There's no doubt that ARM does a very good job, their standard cores are good and the license fees are not huge. Thee are, as you say, thousands of MCUs available using them. It's a different matter if you want to customize the CPU core or build your own. And their 64 bit offering is incompatible with 32 bit and has much bigger code size (no Thumb equivalent).
But worth keeping an eye on RISC-V.