With reference to the (2010) answer to the MultiSite WP install question, there’s the statement:

You cannot choose Sub-directory Install in the following cases:
If your existing WordPress installation has been set up for more than a month, due to issues with existing permalinks. (This problem will be fixed in a future version.)

Some years have elapsed since the answer was posted, are we close to the future version yet?

Over here, the option never came up in the first attempt of multisite WP installation. So, at this moment the default choice given is a Sub-domain installation that comes with the caveat of the prohibitive cost of a wildcard sub-domain. Not a desirable outcome, when all that is required here is one subdirectory overriding the main site SSL cert with the following code in the .htaccess file:

RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization}]
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]

Is there a way of prepping a WP Subdirectory install so the existing WP is not completely erased? Perhaps resetting some of the DB items through an admin plugin like WP phpMyAdmin is the way to go, but not sure exactly how to proceed.

Thanks.