A note upfront:
I assume 'early phase of product development' in the question refers to the development of new features into an existing product.
The referenced blog post is also primarily about products in later stage of their product lifecycle. The stage where you've got a product that hopefully got traction and has active users. Some of the users demand new features. Probably the most active users, the ones you really like. Their needs might be special but since you value them you add the features. At the same time the product gets more complex and harder to learn for new users. Ask yourself: Can the number of power users promoting your product compensate for the number of users that sign up and never get active due to the complexity?
A common way is to 'ask' users during user research. While I think it's important to listen to customers it can also kill a product at the same time, if you kind of misunderstand. It's crucial to find the right balance between maintaining the current (core) product and adding new features to it. This balance needs to be analyzed and tailored for each product. I can't think of a general rule of thumb but I have some thoughts:
- start from the product you've got
- watch real users using your product and look into the usage numbers
- what features do they value most?
- iterate on these features first to make sure the UX is outstanding
- do not (never!) neglect your core product!
- listen to users (not only the loudest ones) -> what else do they want?
- look at similar products and competitors
- ask: would users pay (extra) if this feature was there?
- prototype a new feature and show it to real users
- do they just like it or do they love it?
- decide whether you need to iterate on the prototype or implement it
- consider implementing it for a small group first
- based on the feedback, kill it or keep iterating on it
- give the new feature a seat in the back (i.e. not in the main nav)
- do promote it to a front row seat until the new feature has proven to be great
Besides the standard techniques for testing a feature wireframe or prototype and collecting feedback from users I'm not really sure if there is a particular UX technique for prioritizing features.
Assuming there is a bunch of potential features one could evaluate various aspects in a matrix, like
- fit with core product
- fit with general product vision/strategy
- demand/amount of user feedback
- revenue potential
A note on Minimum Viable Product:
I think the MVP concept is great for startups looking to create a new product from scratch, and for companies that already took the decision to add a particular feature now defining the scope of it.