> dominated by Intel because there was a standard configuration
Perhaps this is part of it, but I think that the more salient point is that not many attempts have been made to make and offer "server-class" ARM systems. The PC desktop/server world has been constantly evolving its Industry-Standard Architecture, bringing in new types of memory, buses and peripheral interconnect the whole time it has existed. By contrast, ARM systems tend to favour the System-on-a-Chip approach, with features that are much more suited to embedded applications than being at the centre of a peripheral-focused/interconnected ecosystem. So you tend to see soldered-on RAM instead of pluggable DIMM chips, vendor-specific emmc storage (there are no standards surrounding how to interface with this class of flash memory) and no sign at all of standard PCI, SATA buses unless it's bolted on as an afterthought (daughter card going over USB, say).
For years, this has been fine. Nobody (apart from uninformed end users who, eg, expected their Windows ARM tablets to be a drop-in replacement for their x86 equivalent) expects the ARM systems that they buy to have a PC-like ISA, apart from some obvious consumer-level interfaces like VGA/HDMI/USB. Also, all these ARM vendors have been working in their own niches with little incentive to rally round some kind of ISA for more "internal" components (equivalents to DIMM, PCI, SATA, RAID controllers, discrete GPUs, etc.). It's only recently that ARM chips/SoC are beginning to be viewed as potential competitors in the PC-like/data centre role thanks to constant improvements in single-core performance, plenty of cores, and the step up to 64-bits. And, of course, energy efficiency compared to x86 legacy systems.
I'm sure that ARM in the data centre is definitely only a case of "when", not "if". I think that the author is right that this SBSA initiative will be a huge step forward for getting vendors to rally around and produce more PC-like architectures, but I think that it's only part of the way. You need standardisation not only at the SoC level (having a standard build configuration so you know how to address all the MMIO registers and such), but also at the level of having standards for physical/electrical interconnects for pluggable DIMMs and PCI-like peripherals.