Is the topic particle は sometimes interchangable with けど?

Question

By the end of the article here, the author means that けど is used for "Introductory remarks: to bring up some topics", such as,

明日｛あした｝だけど、待｛ま｝ち合{あ}わせ時間｛じかん｝どうする？

麻理｛まり｝の誕生日｛たんじょうび｝のことなんだけど、どうする？

彼｛かれ｝のことだけど、聞｛き｝いた？

Wouldn't the sentences have the same meaning as say,

明日｛あした｝は、待｛ま｝ち合{あ}わせ時間｛じかん｝どうする？

麻理｛まり｝の誕生日｛たんじょうび｝のことは、どうする？

彼｛かれ｝のことは、聞｛き｝いた？

I've noticed if I were to substitute は, then I would remove だ and なんだ. Does this mean that by using は, there's less "emotion" and makes the sentence more neutral-sounding?

On the contrary, say that I have some sentences such as,

私はトムです。

これはペンです。

then would it be appropriate to say the following?

私だけど、トムです。

これだけど、ペンです。

Answer 1

は is used to specify the topic that has been already brought up in the discourse, whereas けど is used to give an introductory remark before diving into the main theme. If you said "麻理の誕生日のことはどうする?" at the very beginning of a conversation, it can sound unnatural and sudden. It can sound as if you were assuming the listener had been thinking about Mari. Using けど is more natural as the starter of a conversation.

これだけど、ペンです。
Interested in this thing? It's a pen!
Look at this thing, it's a pen!

These are obviously free translation, but I hope you can catch the nuance. A sentence like this is not impossible, but it sounds like you are explicitly drawing attention to "this object" before disclosing it's actually a pen. You may occasionally want a sentence like this, but you should not think it's interchangeable with は.

Also note that が/けど/けれど are more commonly used with a longer clause rather than a simple noun. In such cases けど is obviously not interchangeable with は. See this question for example.