The proposed change to the qualifying threshold for claiming unfair dismissal from one year to two years will not affect your ability to dismiss unproductive staff, it will simply change the point at which they can challenge you about it. The same holds true for the proposed fees for bringing a claim before the employment tribunal.
There has been a proposal put forward to the government to remove or restrict the rules on unfair dismissal in order to allow employers to dismiss unproductive workers without explanation, although there would be a set financial payment for this similar to redundancy. This has not yet been reviewed or debated and is not a government proposal at this time.
None of these proposals would change the right to claim discrimination so any decision may still be open to challenge which will be easier to defend if you can show that you have followed a clear procedure and made a reasonable decision in the circumstances.
There are already procedures in place that you can follow if your employees are underperforming. If a member of staff is underperforming you should try and determine if there is a reason for this which can be corrected or if dismissal is the only fair option left in the circumstances.
It is worth remembering that you originally believed that these employees would be an asset to the company. It is in your own interest to see if their performance can be improved so that they are as productive as you want and believed they could be before seeking to remove them and incurring the costs of replacing them with someone else who is an unknown quantity.