There are no future standards and trying to guess at what may be required over the expected lifetime of a new facility is somewhat fruitless. That does not mean that some initial accommodations are not worthwhile, but it may be more important to accommodate the future with approaches such as oversized or extra conduit than it is to try to accommodate it with actual cabling. This may also affect the conduit concept, for example you may decide to run from FOH to some intermediate boxes at the stage and other critical locations rather than point to point so as to allow for easier additions, revisions and reconfiguration.
You can never have too many of anything. Obviously, what that involves depends greatly upon your application as that will affect the signal types involved, reliability and redundancy required, etc. CAT5/5e/6 is becoming a common need and is easy to accommodate a few extra. There may be some decision here, a CAT5 cable could potentially serve for data, video, audio, control or other uses so from that perspective it makes much more sense to run a couple of CAT cables rather than multiple dedicated lines. However, this also them ties you into purchasing the appropriate interface devices to be able to use those lines, which may offset much of the savings. But I would probably pull a few extra anyways. Some people are going to fiber rather than CAT cabling. This makes sense for some applications and will probably be more common in the future, but it can be an expensive proposition to incorporate now if you go beyond simply running and terminating the fiber.
You can accommodate some future proofing in the cabling used. Using audio and video cabling appropriate for digital signals may cost more than using generally equivalent cable for analog signals, but may offer some performance advantages and provides for compatibility with future digital sources. That is assuming those don't also change, which is one of the real issues, you can plan for the future but by the time that becomes relevant for you, what you planned for may have been superseded. There is no way to know this as it depends not only on what new technology may bring, but also upon at what unknown time in the future any such changes may occur. For example, many people jumped into DVI only to have it greatly being supplanted by HDMI which in a few years may be replaced by something else. And even different versions of HDMI incorporate different cable requirements, so what was put in a few years ago may not support the latest standards.
A somewhat separate issue is providing additional capacity for near term use, such as planned expansion, or for redundancy. That maybe desired regardless of what is done to accommodate the future and may be determined greatly by what the current system requirements are. For example, if you have 24 mic lines and 8 line level lines from FOH to the stage, you may want to run 30 mic lines and 10 or 12 line level lines so that you have room for growth and the ability to deal with a line going bad. But it may be more difficult to justify running two RGBHV lines to the projector.
