[Note: I really don't know much about psychology / pscyhiatry, so please excuse my ignorance.]
Most 19th century medicine is considered 21st century bullshit--and I think it's pretty likely that three quarters of today's psychology / psychiatry will also become regarded as mostly bullshit.
Today, it's Asperger's Syndrome. Decades from now, that disorder might be broken down into 10 different diosrders and 100 different varieties. Todya's system of diagnosis will almost certainly become regarded as a bunch of misleading generalizations.
Not to mention the fact that nowadays, psychology tends to promote society's values and ideals--and those values and ideals are subject to change. Working a normal job, valuing material things, avoiding most forms of unusual behavior--these qulaitites are part of modern psychology's ideal. But a century later, many or most alternative values might be considered just as sane as today's standard ones.
And the goal of psyschology might change considerably. It currently aims to produce certain types of happiness, and a conformance to certain social norms. But in 2050, the 2011 ideal of hapiness might be regarded as greatly unblanaced
The treatments used by psychologists and psychiatrists will almost certainly undergoe dramatic changes over the next few decades. Today's anti-depressants might become widely regarded as not much different than recreational drugs. A huge chunk of today's widely used psychiatric drugs will almost certainly be considered as harmful or more hrmful than they are beneficical--a mere exchange of one suicidial tendency for another one, a reduction of one flaw and an increase in another, calmer nerves accompaned by __, etc.
To be continued
I'm actually a little skeptical of the current system in place.
For starters, I think most of today's disorders will eventually be broken down into dozens of much different varieties. People who have the "same disorder" nowadays often don't really have that in common.
I'm not so sure I agree with the basic philosophy behind abnormal psychology. It tends to promote a particular society's values and ideals.