There are various competencies you need to demonstrate to become a partner, but there's enough diversity between them that most businesses with Microsoft tech somewhere in the stack could become a partner.
If you are an ISV producing code that runs using Microsoft tech on Windows, it is not particularly difficult at all to qualify as at least a Silver-level partner. It's kind of a PITA to run your applications through the verification process every couple of years, but it's not hard, more tedious; or you can get a couple people to pass some of the certification tests.
https://partner.microsoft.com/en-AU/membership/msdn-subscrip...
The registration fee is something like $2K.
There are various competencies you need to demonstrate to become a partner, but there's enough diversity between them that most businesses with Microsoft tech somewhere in the stack could become a partner.