Marketable skills are a good thing, certainly, but the argument you're making fails to account for the increasing capabilities of automation.
The ability to automate a job derives from the degree to which it is possible to map out job tasks in a clear pattern.....
In a Slashdot-friendly area, consider devops - it used to take a lot more *nix engineers to manage large installations than it does now. A few devops engineers now can manage tens or hundreds of thousands of servers using mcollective, puppet, chef, ansible, salt, et cetera. So that reduces demand for traditional SA except in corner-cases where a particular configuration needs to be debugged at a level deeper than the DevOps staff can do. Those are marketable skills which are being undermined by automation.....and they are not low-skill jobs.
We know that low-skill jobs are going to be automated - truck driving, package handling, much fast-food restaurant work, assembly work, et cetera. This is going to accelerate the reduction in demand for the average low-skill worker well beyond the labor-arbitrage-based outsourcing that they've suffered to date. The jobs will not be going elsewhere; they'll just go away. This is the logical end result of business - they want their labor expenses to be zero, or as close to zero as possible (hence the continued presence of slavery throughout the world, including the US), and if there's a way to replace a labor expense with a capital expense - a robot or automation system - business will automatically do that. Why? Because they're incentivized to - capital assets do cost money, but they depreciate and provide tax advantages and generally don't involve litigation, unless the business runs into a dispute with a vendor, which is way less risky than any labor-related litigation.
The net end goal is the reduction of jobs to as few as possible to enable the maximization of profit for business entities. This will tend to concentrate the wealth among the owners and the relatively few workers whose jobs can not be automated, which will be a fairly small subset of the population. The rest will be left to fend for themselves in an economic system where a lack of long-term employment is equivalent to extreme privation, loss of material goods, housing, access to capital, access to health care, et cetera.
There's already a lot of evidence to show what happens when the jobs go - look at the formerly industrial northeast and midwest, where plant closings have plunged communities into abject poverty overnight, killing property values, driving up foreclosures, despair, and poor behavioral choices - not least of which is blaming undocumented immigrants rather than the executives who made the decision to engage in labor arbitrage.
TL;DR: If your job can be automated, no amount of marketable skills will remain marketable. And that includes you, most SAs, unless you're lucky enough to get a senior devops position. So maybe we should consider a strong social safety net to deal with the inevitable fallout from automation rather than suffering through the chaos that it will cause....