I think that's because rents have been low or lowish for the last while - the lack of negotiation, I mean. If they start to rise in a crazy fashion, then there could be problems...
That being said, I was interested during the weekend to notice the lack of difference between rents in the outlying areas versus rents closer to the city. If you had 1300E to spare, worked somewhere in the north city/county area, are you going to pay 1300E in Swords when you could pay the same in Dublin 9? For me the answer is no. So if rents in towards the city don't go up, I don't expect rents outside the city to stay where they are.
I don't think that you need to start negotiating really, it's a question of looking at what your money will buy you by way of rental property if you're a renter. Again, 900E for a one bedroomed apartment in D9 versus the same in Swords? If you look around and find better value else where, the market will change. A lack of interest does nasty things to the market
The other point is, all landlords asking increased rent can only work if there's an excess of tenants over landlords. TBH, I'm not sure there is, even now. I've no trouble finding houses at the moment, but I can have issues finding house-sharers. I think there's more property than tenants at the moment, and I think the ones who are looking to reduce their exposure to subsidising their tenants are in for a nasty shock. 1300E in Dublin 9, because so little of it is new, may well be more than profitable for the landlord because they were bought much longer ago than people buying into new estates, taking rental hits because property values will go up and absorb that.
IMO, it'll be interesting to see what happens when some investors realise that capital appreciation won't offset their rental losses, particularly those ones who don't bother renting out their property because they thought that capital appreciation was all they needed. They'll either 1) sell fast or 2) start renting. In the latter case, they'll be coming into a market which is already shored up courtesy of the HSE payments and which is already oversupplied with property and undersupplied with tenants. If the number of immigration construction workers takes a hit too the number of tenants will further fall (not fully convinced about the latter courtesy of infrastructure building which continues to go on).
My guess is that sometime shortly a lot of them will sell out, with two effects: 1) drop in some property sales values and 2) drop in rental property availability. I expect rentals to hit equilibrium a bit before property prices do, but frankly, that's based on a gut instinct and could well be wrong. I'm just not convinced about the desirability of those properties as an FTB. I've looked at far too many concrete jungle poorly designed badly laid out estates with less than perfect apartments in them. I'm interested in seeing what's going to happen.