In essence the Kilo class submarines can deploy tube launched Klub-S missiles only and do not offer any specific growth options. Beyond that the Type-209 torp tubes can easily accommodate ASCMs/ASMs like the Harpoon with some tweaks (Chang Bogo upgrade for the South Korean Navy subs and even the IN has expressed interest in similar plans to equip the Shishumar class subs with the Block-2 harpoon variant-
Navy plans missiles for four submarines - Indian Express). Such an upgrade would invalidate any concern regarding the lack of ASM/ASCMs aboard the sub and bridge the gap wrt Kilo subs. The Kilo's ability to operate with the Klub missile complex (tube launched, after refit), with the Klub-S's relatively superior range, was advantageous for littoral anti shipping ops but he Shishumar operating with the Harpoon and AIP plug-in can do the same just as well.
For concerns regrading how operationally suitable a Type-209 submarine shall be in the future while lacking any VLS capability:- There is a reason why the Scorpene does not have any VLS modules for CMs and will not have any either despite anyone's wishes (in fact the 533 mm torpedo tubes on the Scorpene will ensure that no large CM can be employed whatsoever even if they be tube launched- short of the Exocet or Harpoon ASCMs). The reason is quite simple, the requirement for CM (apart from tube launched ASCMs) launch capability on SSKs is primarily predicated upon the non-availability of larger nuclear powered platforms which can perform such operations far more effectively (best example:- Type 032 subs being built for export purposes to countries which cannot and will not be able to build/acquire nuclear marine platforms). This is the same reason why all future conventional submarines from the Type-216 (which MAY have a planned VLS module IF the Australians pick it for the Collins replacement program) and the A-26 to the S-80 do not require VLS modules (thus allowing only the use of certain types of ASCMs). A Scorpene launching an Exocet, which due to being housed within a VSM can be launched from deeper depths, is far more suitable for discrete submarine operations against surface combatants in littoral waters.
As we move into the next decade SSKs, which primarily operate in littoral waters, will have no business operating with LACMs (in case someone wants to fit in a land attack variant of the Brahmos on a SSK) or very heavy ASCMs- an exocet or harpoon will do the job just as well. Unless there is a specific case made for the sub-launched Brahmos being operated from select conventional platforms, which still would be more suited on board a SSN.
Furthermore, you must take note of the fact that as we sit on our hands the window of opportunity to use the dearly bought know how and know why wrt Type-209 diminishes. Also once you have the know how and the know why in hand, up-scaling a design is as easy as manufacturing the original variant- specially when the design has been up-scaled by the OEM successfully before.
Bare in mind that the Kilo subs are larger but even they do not offer VLS launch capabilities and the Klub variant primarily found on them (3M-54E1) has the same performance parameters as the Harpoon block-2 as such.
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Abingdonboy something to add perhaps?