In my opinion your pond can do with your intended airline. Whether you install it on the window or far side will both look good. The air will be aesthetically pleasing to your guests while the aeration will benefit the Koi.
Following are a few points to consider when installing your airline;
1. Seventeen meter airline run is really long! A considerable volume of air will be needed to give the desired effect. Be mindful when selecting the pump or pumps used. As an example I run two air stones, one 1,2 metre underwater air curtain and a perforated pipe supplying air to the biological filter, all off one 120 litre per minute air pump. In this setup I need to carefully tune the supplies otherwise the air curtain simply grinds to a painful halt. The deeper the airline under water the more potent the pump needed to work against the water pressure. Incidentally, if your airline is not 100% level the resulting bubbles might be concentrated at one end only with the rest of the line suffering from air deprivation.
2. On the topic of noise. Koi like humans can hear so I believe that, like with us, excessive noise will irritate them and may contribute to increased stress. An airline in the pond will definitely create noise. Firstly the line itself will vibrate when air is force fed through it, this vibration might be so severe that the airline could drum against the side of the pond potentially creating a night club like cacophony for your Koi to enjoy or not. This phenomena is cause to consider using a rigged airline which is secured to the pond wall.
3. Furthermore the pump itself creates noise which will certainly be fed, via the airline, to the pond; again for your Koi to dance to if they so wish. My diaphragm air pump is used 24/7 in my pond (Eskom permitting) I also have a piston type for the quarantine pond. The latter was switched on once and due to the resulting noise, promptly off again. If I cant stand the noise the Koi likewise, I reasoned. As a by the way, this pump is available if anybody is interested.
4. Now the question; what pump to use? In my opinion a diaphragm pump is the best choice considering volume of air produced and silence in operation. The most potent diaphragm pond pump that I have seen delivers 160 l/m which I doubt is enough volume for the 17 metre airline, so a number of these, on separate lines, might be needed. The jury is in sitting to discuss this issue. Then there is the piston type as mentioned. Maybe the compressor type (as used at service stations) warrants consideration, a vast amount of air can be made available and if positioned some distance from the pond the noise audible to your Koi and guests might be reduced (?).
Now after all that rambling of yours truly:
In my opinion the simplest solution is to use medium size air stones with a configuration of diaphragm air pumps to obtain a balanced bubble display. The sight of tubing running into the water might be highly undesirable to the point of being obnoxious; in which case escape, cancel and delete this option.
Ask the breeders, dealers and Koi keepers that aerate large ponds how it is done. Our esteemed administrator and my partner in Silkworm International; Paul and others come to mind.
Consider the compressor option. Does compression build up toxic gas?
Surely there must be some experts in this field that can advise (at a price of cause). I am thinking of those spectacular water displays observed in the lobbies of some fancy office buildings. As long as they consider both the Koi and the aesthetics!
PS How many Koi in your pond?