Okay, let's assume Funcom could add a solo raid that drops 8 T4 relics. What should that solo raid be like to equate to doing T4?
First, it should be of such difficulty that the player likely dies on the first boss for a good three months before he has the strat down to defeat it.
Second, the rest of the bosses would not be hard to defeat, but would need items to click, AA feats learned (and used at the appropriate time or else the player will die), additional gear sets and feat specs to switch into, or be timed with a guaranteed fail if not defeated before the timer ran out.
Third, it should take a solo player a solid 4 hours time (probably more) to progress through the entire instance.
Fourth, while one can get 8 relics by completing the instance, chances for gear drops and dragon tears should be low - certainly no more than a 5% chance of gaining a useful piece of gear or dragon tear.
That might be a fair way to have a solo instance provide T4 gear to someone who doesn't do T4 raiding. Otherwise, players will just do the solo instance and filling T4 raids will become problematic.