I think you made some good points Rodrigo. Here is my attempt at a routine along that line.

InstallMathematicaApplication::usage = 
  "InstallMathematicaApplication[\"URL\"] will download and install \
the application zip file located at the URL address into your \
$UserBaseDirectory/Applications folder. The installation path to the \
first item installed, which will usually be the application folder, \
is printed.";
SyntaxInformation[
   InstallMathematicaApplication] = {"ArgumentsPattern" -> {_}};
InstallMathematicaApplication[URLLink_String] :=
 Module[{modifiedURL, tempFile, application},
  modifiedURL = StringReplace[URLLink, "?dl=0" -> "?dl=1"];
  tempFile = URLSave[modifiedURL,
    FileNameJoin[{$UserBaseDirectory, "Applications", 
      "ApplicationDownload.zip"}]];
  application = 
   ExtractArchive[tempFile, 
     FileNameJoin[{$UserBaseDirectory, "Applications"}]][[1]];
  DeleteFile[tempFile];
  Print["Application installed at: ", application]
  ]

It is specialized to installing zip files into the `$UserBaseDirectory/Applications folder. But there is one problem with the ExtractArchive command. It will fail if any existing files exist. So one can't use it to update. As far as I'm concerned WRI should fix that, perhaps using an option. Right now I'm supplying my packages from Dropbox. If one creates a user link for a zip file, Dropbox ends it with ?dl=0. ExtractArchive will not work on that. So I change it to ?dl=1 in the routine.

Here is a test case you can try. It contains a rather worthless stub application I abandoned. So you could delete it after the test.

InstallMathematicaApplication["https://www.dropbox.com/s/\
kin3ajodnys92n8/ConicSections.zip?dl=0"]

`

Wolfram Research has set up a quite adequate method for writing and using packages or applications, but they have done a poor job of communicating it.

These should probably be called 'applications' rather than 'packages' because an application may contain several or no packages, and it can contain other components besides packages, such as documentation, style sheets, palettes and application notebooks. It is very easy for a potential user to install an application. Just send them a zip file that they unzip directly into their $UserBaseDirectory/Applications folder. That's it. Unzip and immediately use it.

I've written an extensive tutorial on writing applications at A Mathematica Style.

I believe that you can already do this within Wolfram Language. All you need to do is to build (or find) a package (a .m or .wl file) and save it to the appropriate directory. On the desktop, there is the $UserBaseDirectory that will work, although saving into the Applications folder/directory inside this directory is probably better. For the Cloud, there must be an analogous place to store packages.

You could probably write your own function, installPackage[], that will do exactly what you want to do.