It doesn't seem like a stretch to assume that the building rate will go down, and prices on older estates not affected by the law will go up. Unless the law is applied broadly across any and all estates, the end result will simply be, best case, that the market adjusts: worst case, that you end up with very unwanted and negative economical effects that no-one predicted.
The article states that "It’s not yet been clarified, for example, how long an owner would have to occupy their home before being able to rent it out" -- in my opinion the problem here is not where you draw the line, the problem is the drawing of the line. It will only create synthetic movements in the market and I don't think it will help in achieving the stated goal at all.
If one were inclined to be cynical, one could even assume that like with most political proposals, there are those who stand to gain from this, and they may be sponsoring it. Namely: whoever owns "old" real estate in Amsterdam. Is it also cynical to believe that politicians may know that this will not help, but are more interested in looking like they are "doing something about it", rather than resolving the issue, causing economical loss for property owners? The stated beneficiaries of this proposal are those weak in buying power claiming the "right" to live in a certain place without being priced out -- normally not a group with huge political leverage.