What if you beg Dell for a Inspiron that otherwise out-of-service?

Dell will support systems for four years after they're released, which is the longest period for which you can purchase a warranty.  After that time, parts are no longer available.  This is standard in not just the PC industry, but across industries for most consumer products.  

Apple also renders older systems end of life and either no longer provides parts, or in its case, charges so much for the parts that replacement cost exceeds the value of the system.  In fact, price a logic board for a Macbook vs. a mainboard for a Dell/HP/Lenovo/ASUS/Acer/etc system and you'll see that just about any major out of warranty failure on a Macbook will result in it being similar in cost or even less expensive to simply replace the system.

The vast majority of Inspiron systems are sold with a one year warranty and for well under $1,000 -- meaning that within a couple of years of use, the systems become more expensive to repair than replace.

There are plenty of third-party repair sources for PC notebook from all manufacturers.  With Apple, you have only one source of replacement parts -- Apple controls its ecosystem from design to purchase to repair.  

If you're looking for more extensive parts support over time, with Dell, choose Latitude or Precision, not Inspiron, Vostro or XPS -- business class systems change less in design over time, and have longer product life cycles.

Valid answer. Very (extremely) valid.

How many years does a Latitude or Precision known to be offered at least with support, comparably to Alienware, Vostro, XPS or Inspiron/G-Series, especially if these are for business class?

  Dell will support systems for four years after they're released, which is the longest period for which you can purchase a warranty.  After that time, parts are no longer available.  This is standard in not just the PC industry, but across industries for most consumer products.  

For the parts, some of your answer is not correct, as long as, if any problems that rise arose doesn't anywhere relate to the motherboard, which is bound to a Service Tag. Repairs that doesn't relate to a mobo is easy peasy, but if any relates to a mobo, it's a high-risk - high-reward task. Damaged motherboards trash any Dell system that doesn't have a warranty extended to anywhere.

There are plenty of third-party repair sources for PC notebook from all manufacturers.

Vietnamese people typically scrap any PCs into separate parts. For example: this one.

(It's) a Latitude! It's a result of someone scrap a E6320 into separate parts and sell it. People cannot deal a mobo as it had a Service Tag bound with it and having a replacement one is a risky act, so the dealer keep the mobo along with the scrapped system.

Those who want to use that one as a normal laptop only need to simply buy a screen, a battery, a kbd, then the powercord, RAM and SSD and it does literally POSTs.
An laptop's screen can be scrapped into a part for one another. Dell laptop screens are not invulnerable. Batteries can be spared from a laptop into a part, or the battery can be even made by a third party if Dell's no longer available.

Damaged keyboards does literally at a hope as those spare is also sold as a lone part. Someone even dared to sell one for my model, with keyboard both available in white type [AWCC configurable] and orange, all spare. And finally, people also sell spare Dell powercords, or even a Dell cord to PD (GaN) USB-C converter, max. 100W.

So regarding on the instance of desktop classes are, do anyone on the community know about the barebone Dell systems whose also circulating on Shopee anywhere just yet?

I got a dozze of about Optiplex 3070s and some else on the Shopee. Are those "used" or did Dell continue to support these systems to this date? These Dell systems are quite suspected to be having comparably more parts than abnormal. The Shopee also list those "barebone" Optiplexs.

...In fact, price a logic board for a Macbook vs. a mainboard for a Dell/HP/Lenovo/ASUS/Acer/etc system and you'll see that just about any major out of warranty failure on a Macbook will result in it being similar in cost or even less expensive to simply replace the system.
...With Apple, you have only one source of replacement parts -- Apple controls its ecosystem from design to purchase to repair.

For Apple, they're really sucks and, much worse for leaving Team Blue [Intel] behind and declare an era for Apple Silicon. That, and I call those who kept using a Mac or MacBooks sucks more than those stick with your era of Dell, for a reason simple that an Apple system is extremely fragile than a Dell as they cannot resist against 100 of the problems. Once a Mac damaged, you cannot repair - it's a one-time use system, as just like iPhones, iPads or even a AirPods. Nice greeding.

If you're looking for more extensive parts support over time, with Dell, choose Latitude or Precision, not Inspiron, Vostro or XPS -- business class systems change less in design over time, and have longer product life cycles.

Well, as you told, household classes and especially gamer's class are very brutal in part pricing compared to those who intended for those who they're not slacking.