Those discussions do not affect you as a traveller during the middle - late of 2017. Possibly even 2018!
Background. They discovered the discrepancy three years ago and it has taken that amount of time for the vote to be tabled. The European Parliament voted today (3 March 2017) on a non-binding resolution to urge the European Commission to make a decision on it and to implement the various legal measures. The ultimate decision has to come from the Commission, not the European Parliament.
The Commission will reach a decision (likely following the EU-US Summit in June) and if they decide to require Americans to have visas, they will turn it over to the individual member states for implementation. Implementation will take a while, plus the UK and Ireland will negotiate an opt-out.
The implementation will take account of the need for a transition period, and the transition will be phased in. All the transition plans will need to be approved and that will take a while. Then they have to be published with an activation date well in advance. Then they have to hire and train visa officials because bureaucracies always need to staff up when the work load is affected.
The initial design is likely to be something non-intrusive like the US Electronic System for Travel Authorisation (ESTA) and that means they will have to staff up developers to write the software and then make an interface to the airline visa checking system.
Meanwhile at any point the US could come along and say something like, "OK, we'll accept Cypriots into the Visa Waiver Programme". And this could send the whole ball of wax back to the Commission for another vote because the circumstances have changed. It is also conceivable that the US could come along and say "Hey, let's set up a joint task force and have several rounds of high-level meetings about this" and it could go in indefinitely.
It will take a long time. Nobody will be stranded, nobody will be compromised, nobody will be unreasonably bounced for not having a visa.
I'm aware that on-going immigration bans taking place in other regimes may create some anxiety due to lack of planning, but the EU is much more deliberate. In other words, don't worry about it.
Notes and comments
Having seen the UK implement a visa requirement without any
forwarning, (apart from the very early 'there might be a visa needed
in the future') I do not trust on the visa start date being anounced
more than 24 hours before the start of the need of the visa, if that
much. If it is anounced earlier you are lucky, it is not a right
Indeed, the UK made a snap decision to require visas for some countries, but your observation compares apples and oranges. The UK (whether right or wrong) was hoping to stop a rapid influx of people from less affluent countries seeking permanent residence and creating a drain on the public coffers. Those people are not volume customers of the airline lobbies and similarly do not noticeably boost local economies. In this situation, we're talking about tourists and business professionals who visit and thereby boost the local economies via hotels, restaurants, local transport, local attractions, and so on. That's a big difference which has not been accounted for in your observation.
If the EU really decides to retaliate by requiring visas for US visas,
it would do so mainly by amending the relevant regulation. The UK
would be free to opt-out using current rules (i.e. no real
negotiation, just a notification) and Schengen countries don't have to
change anything to their legislation, regulations are immediately
applicable. Like you, I fully expect the EU to be more deliberate and
provide for a delay but the implementation itself does not need to
take more than a few months.
And you're right that the Parliament is basically powerless but the
Commission can't decide to change the regulation alone either and its
decision will not be final, the Council has to be involved. So the
process is not really Commission deciding, state implementing, it's
Commission+states (through the Council) deciding and then the relevant
state agencies/bureaucracies implementing directly. And if there was a
will to go that way (which there isn't as far as I can tell), a
partial decision from the US would not necessarily mean the process
has to restart from the beginning.
Your technical expertise is always welcome. I see you have added an answer here and would advise those following this thread to read it carefully and with the respect accorded to an expert in the field. It's an evolving event and I'll update as things congeal.