Instructables moving to a closed for-pay model
Free Instructables users will not longer be able to:
1) View entire instructables at once
This means that if an instructable has more than one image in a given step, you will only be able to see the first image, and thumbnails of the other images. If the author left important detail in the images, that information is lost.
Further, printing an instructable so you can take it to the workshop or hardware store is essentially removed. You can, if you like, print out each step separately including all the headers, sidebars, ads, footers, comments, and other fluff, but that results in a hard to read page (try it - the layout is not conducive to printing) and a sheaf of paper for a 5 step instructable, including all the wasted ink and time. The images are still not accessible either.
This poses problems for authors who now have to either rework their instructables so viewers from Google (which accounts for a substantial portion of their viewership) and others can actually use it. Otherwise some important details may be lost in secondary images for over 95% of instructables viewers.
Moving to a Closed For-Pay Model
Many, many companies do this, and some actually succeed. CDDB did this to their users, but they lost their community in the process. They still exist doing similar functions, but their original role was filled by open providers.
Geocaching.org did this without losing their community, but they only put new features behind the pay wall, they did not hobble the primary user experience. The community was burned by this, but they made enough concessions to avoid losing the critical mass they needed to operate. Unlike CDDB, Geocaching can only exist and continue with the community.
I'm afraid that Instructables, by removing basic features that are necessary to follow an instructable, and being unable to change their model in a way that would allow them to survive without the community, is ultimately going to decline and lose market share to other services of a similar nature.
Which is a shame. It could take less than 5 years to lose their huge marketshare, and a lot of knowledge will go down with them.