In a realistic setup – such as a growing large city – when everyone enjoys streaming video the congestion of bandwidth will always result in lower speeds.
But wait until many people will start streaming 4K or 8K video, then you will see your Wi-Fi network performance go down the toilet (Netflix is looking at streaming 8K in few years).
Technology is a wonderful thing: you may have noticed there was a 6 years gap to bring to market the Wi-Fi ac which is an eternity in technology terms. It was very expensive and hard to find and now you find it in every premium device. The next generation of Wi-Fi technology is expected for 2018 or later but it is much more to develop and test before we will see the first device available.
In summary, when planning to build a house it is recommended to work out the best combination between using Wi-Fi technology and installing sufficient cabling around the house to provide that infrastructure no matter what/when changes will happen in technologies and their associated costs. As explained above, upgrading your router will not be sufficient as any Wi-Fi network will be impacted by congestion and its slowest link (not many people will change their devices every 5 years). Therefore having a Lynxnet structured cabling system will prevent many future issues in your network performance.