Can ArcGIS Server Ever Really Replace ArcXML?
That being said, I have seen ArcGis Server come a long way since that initial 9.0 release. 9.3 shows lots of promise, and I am especially impressed with the new javascript and REST api's. For most folks out there that have to produce apps on a regular basis, the web adf has been a disaster. Its simply not easy (compared to ArcIMS/ArcXML) to create complex, on the fly maps. Period. I dont think there is much argument to that point.
My coworker came in my office this morning and said "What do you think about migrating the xxx app over to ArcGIS server 9.3 stuff you have been crowing about?" My first thought, was yeck yeah, that would be cool. Its just some simple maps displaying some simple geography with nothing fancy going on. Perfect fit for the new 9.3 Javascript/REST API. But, then it occurred to me...to make those 'simple' maps, we are doing some very tricky ArcXML to get the right data displayed on the fly. You know they type - we have all done it - something that really pushed ArcXML to do something very cool. Its probably a lot more than the creators of ArcXML ever intended.
Then I thought about it more...how in the world would I do this with ArcGIS 9.3? Use the web adf to display a simple map? Nope. Not a chance. Use REST? Well, its nowhere near ready to take on these types of crazy requests that we can do with ArcXML (like on the fly rendering, etc). In the past, we could massage that ArcXML to do just about anything we wanted. The downside was we didnt get that instant gratification of a ajaxy map that AGS 9.3 gives. The general public now demands the ease of use and speed that The Google gives us.
So, where does this leave us? In a tough spot. AGS still isnt ready to create those cool on the fly maps (not everything can be cached you know!) that we could do with ArcXML. My hope is that the ESRI REST implementation will continue to grow, as I'm sure it will. But, will it ever be able to achieve that ArcXML status? My thinking is that ESRI is going to keep ArcXML around for a long time to come and it will be integrated into future releases of ArcGIS Server. There must be some middle ground here. I'm sure they have already thought about it plenty, but now is the time to act.
But, I really should have stressed just how happy I have been with 9.3 and the js/rest api. I think ESRI understands how important it is to get this thing right and continue to extend its capabilities. If I were you, I'd hold tight and wait for 9.3, its pretty awesome.