Could, yes, but it's not as easy as you'd think due to the fact that we're using power amplifiers. It would require a few extra components that would increase the cost of the Almond+ and we'd have to figure out a way to switch between the antenna outputs easily. As for the power amplifiers, if you remove the antenna on a router with power amplifiers you can and most likely will damage the router permanently if you power it on like this.
We've had a fair bit of feedback on Kickstarter about this and it's something we've looked into, but as of right now I don't think it'll be included.
This advice is definitely accurate. This is why CB Radio technicians used "dummy loads" on CB Radios when servicing them. (Does anyone around here remember CB Radios? I retired all my Citizen Band radios more than 20 years ago).
As you increase the DBi "gain" of the antenna, you need to reduce the dBm amplification of the Radio, in order to remain within Regulatory compliance. People that fail to understand this when using external antennas may end up getting visits from their Governments, for operating non-compliant equipment. Such visits are never fun.
A misconfigured Transciever can cause havoc on neighbouring (compliant) trancievers, (including Emergency 911 Dispatch services), so the penalties for operating in this fashion can be severe, and some jurisdictions may penalize the guilty party, even if they were not aware that their equipment and/or configuration of their equipment was causing the issue.
You can't simply install higher gain antennas without understanding this. If you aren't familiar with radio and antenna theory, then you should enlist assistance from a local HAM Radio operator to ensure your equipment is still regulatory compliant. The fines for operating non-compliant equipment can be severe indeed. Here in North America, we can only operate at 1W with standard 3-5dBi antennas (the most common type in most routers I'm aware of), but we can lower our power to 0.25W and upgrade to a 24dbi antennas for point-to-point Wi-Fi connections in order to get an effective (narrow-beam) power of 60W at the antenna. Most consumers want omni-directional antennas (to maximize Wi-Fi coverage area), so this does not apply to most consumers as they aren't setting up point-to-point Wi-Fi networks. (This technique is common in large Wi-Fi Mesh networks though).
This technique when used with Yagi antennas can make a Wi-Fi connection go for Miles/Kms. Check your local regulations to see what is possible within your regulatory area. Again the penalties for non-compliance can be severe. Personally I choose to stick to the manufacturers design, as this allows me to blame the manufacturer rather than myself if my equipment is ever questioned.
Power boosters, (not provided by the OEM (Original Equipment Manufacturer)) can lead to serious fines. As Lars stated compliance isn't as easy as some might like to believe.